chore: cleanup unused imports

Closes #17

.github/workflows/ci.yml

@@ -0,0 +1,106 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  tests:
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+          - windows-latest
+        rust:
+          - 1.59.0 # msrv
+          - stable
+          - beta
+          - nightly
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Restore cargo cache
+        uses: actions/cache@v2.1.7
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ matrix.os }}-cargo-${{ matrix.rust }}-${{ hashFiles('Cargo.lock') }}
+
+      - name: Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.rust }}
+          override: true
+
+      - name: Run tests
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --all-features --verbose
+  
+  clippy:
+    name: clippy (ubuntu-latest, stable)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+          components: clippy
+
+      - name: Restore cargo cache
+        uses: actions/cache@v2.1.7
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-stable-${{ hashFiles('Cargo.lock') }}
+
+      - name: Check clippy
+        uses: actions-rs/cargo@v1
+        with:
+          command: clippy
+          args: -- -D warnings
+  
+  fmt:
+    name: fmt (ubuntu-latest, stable)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+          components: rustfmt
+
+      - name: Restore cargo cache
+        uses: actions/cache@v2.1.7
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-stable-${{ hashFiles('Cargo.lock') }}
+
+      - name: Check format
+        uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check

Cargo.lock

@@ -4,4 +4,4 @@ version = 3
 
 [[package]]
 name = "estring"
-version = "0.1.2"
+version = "0.3.0"

Cargo.toml

@@ -1,19 +1,15 @@
 [package]
 name = "estring"
 description = "A simple way to parse a string using type annotations"
-version = "0.1.2"
-edition = "2018"
+version = "0.3.0"
+edition = "2021"
 authors = ["Dmitriy Pleshevskiy <dmitriy@ideascup.me>"]
 readme = "README.md"
 repository = "https://github.com/pleshevskiy/estring"
 license = "MIT"
 keywords = ["parsing", "type", "annotations", "customizable"]
 categories = ["data-structures", "parsing"]
-
-# rust-version = "1.51.0" # The first version of Cargo that supports this field is 1.56.0
-
-[package.metadata]
-msrv = "1.51.0"
+rust-version = "1.59.0"
 
 [package.metadata.docs.rs]
 all-features = true
@@ -21,12 +17,9 @@ all-features = true
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [features]
-prim = ["number", "bool"]
-number = []
-bool = []
-vec = []
-tuple = []
 low-level = []
+aggs = []
+structs = []
 
 [dependencies]
 
@@ -35,8 +28,8 @@ maintenance = { status = "actively-developed" }
 
 [[example]]
 name = "calc"
-required-features = ["vec", "number"]
+required-features = ["structs", "aggs"]
 
 [[example]]
 name = "dotenv"
-required-features = ["vec", "tuple", "low-level"]
+required-features = ["structs", "low-level"]

README.md

@@ -1,18 +1,45 @@
 # EString
 
-[![docs.rs](https://img.shields.io/docsrs/estring?style=flat-square)](https://docs.rs/estring)
 [![Crates.io](https://img.shields.io/crates/v/estring?style=flat-square)](https://crates.io/crates/estring)
-[![Crates.io](https://img.shields.io/crates/l/estring?style=flat-square)](https://github.com/pleshevskiy/estring/LICENSE)
-[![unsafe forbidden](https://img.shields.io/badge/unsafe-forbidden-success.svg?style=flat-square)](https://github.com/rust-secure-code/safety-dance/)
-[![Matrix](https://img.shields.io/matrix/enve_team:matrix.org?label=matrix&style=flat-square)](https://matrix.to/#/!yZalHbWfGRWOMaetSn:matrix.org?via=matrix.org)
+[![docs.rs](https://img.shields.io/docsrs/estring?style=flat-square)](https://docs.rs/estring)
+[![GitHub Workflow Status](https://img.shields.io/github/workflow/status/pleshevskiy/estring/CI?label=tests&logo=github&style=flat-square)](https://github.com/pleshevskiy/estring/actions/workflows/ci.yml)
+![The MSRV](https://img.shields.io/badge/MSRV-1.59.0-red.svg)
+
+```toml
+[dependencies]
+estring = "0.3"
+```
 
 A simple way to parse a string using type annotations.
 
-This package was originally designed for [enve]
+This package was originally designed for [enve].
 
 [enve]: https://github.com/pleshevskiy/enve
 
-## Getting started
+## [Documentation](https://docs.rs/estring)
+
+For more details, see [examples].
+
+[examples]: https://github.com/pleshevskiy/estring/tree/main/examples
+
+## Usage
+
+Basic
+
+```rust
+use estring::EString;
+
+fn main() -> estring::Result<()> {
+    let res: i32 = EString::from("10").parse()?;
+    assert_eq!(res, 10);
+    Ok(())
+}
+```
+
+You can use predefined structs like `SepVec` if you enable the `structs`
+feature.
+
+Note: You can use custom types as annotations! Just implement `ParseFragment`!
 
 ```rust
 use estring::{SepVec, EString};
@@ -20,7 +47,7 @@ use estring::{SepVec, EString};
 type PlusVec<T> = SepVec<T, '+'>;
 type MulVec<T> = SepVec<T, '*'>;
 
-fn main() -> Result<(), estring::ParseError> {
+fn main() -> estring::Result<()> {
     let res = EString::from("10+5*2+3")
         .parse::<PlusVec<MulVec<f32>>>()?
         .iter()
@@ -32,27 +59,30 @@ fn main() -> Result<(), estring::ParseError> {
 }
 ```
 
-You can use custom types as annotations! Just implement `TryFrom<EString>`!
+You can also use predefined aggregators if you enable the `aggs` feature.
 
-## Installation
+```rust
+use estring::{Aggregate, EString, Product, SepVec, Sum};
 
-**The MSRV is 1.51.0**
+type PlusVec<T> = SepVec<T, '+'>;
+type MulVec<T> = SepVec<T, '*'>;
 
-Add `estring = { version = "0.1", features = ["vec", "number"] }` as a
-dependency in `Cargo.toml`.
+fn main() -> estring::Result<()> {
+    let res = EString::from("10+5*2+3")
+        .parse::<Sum<PlusVec<Product<MulVec<f32>>>>>()?
+        .agg();
 
-`Cargo.toml` example:
-
-```toml
-[package]
-name = "my-crate"
-version = "0.1.0"
-authors = ["Me <user@rust-lang.org>"]
-
-[dependencies]
-estring = { version = "0.1", features = ["vec", "number"] }
+    assert_eq!(res, 23.0);
+    Ok(())
+}
 ```
 
+## Contact Us
+
+Join us in:
+
+[![Matrix](https://img.shields.io/badge/matrix-%23enve_team:matrix.org-blueviolet.svg?style=flat-square)](https://matrix.to/#/#enve_team:matrix.org)
+
 ## License
 
 **MIT**. See [LICENSE](https://github.com/pleshevskiy/estring/LICENSE) to see

examples/calc.rs

@@ -1,14 +1,12 @@
-use estring::{EString, SepVec};
+use estring::{Aggregate, EString, Product, SepVec, Sum};
 
 type PlusVec<T> = SepVec<T, '+'>;
 type MulVec<T> = SepVec<T, '*'>;
 
-fn main() -> Result<(), estring::ParseError> {
+fn main() -> estring::Result<()> {
     let res = EString::from("10+5*2+3")
-        .parse::<PlusVec<MulVec<f32>>>()?
-        .iter()
-        .map(|m| m.iter().product::<f32>())
-        .sum::<f32>();
+        .parse::<Sum<PlusVec<Product<MulVec<f32>>>>>()?
+        .agg();
 
     assert_eq!(res, 23.0);
     Ok(())

examples/dotenv.rs

@@ -5,7 +5,7 @@ DATABASE_URL=postgres://user:password@localhost:5432/recipes
 APP_HOST=http://localhost:3000
 ";
 
-fn main() -> Result<(), estring::ParseError> {
+fn main() -> estring::Result<()> {
     EString::from(DOTENV_CONTENT)
         .parse::<Trim<SepVec<Pair<&str, '=', &str>, '\n'>>>()?
         .iter()

src/agg.rs

@@ -0,0 +1,8 @@
+//! This module will contain aggregate functions (Sum, Product, etc)
+//!
+
+mod product;
+mod sum;
+
+pub use product::*;
+pub use sum::*;

src/agg/product.rs

@@ -0,0 +1,92 @@
+use crate::{Aggregatable, Aggregate, EString, ParseFragment};
+
+/// Aggregate struct, that can multiply inner aggregatable [items](Aggregatable::items) if
+/// [``Aggregatable::Item``] implements [``std::iter::Product``](std::iter::Product)
+///
+/// # Examples
+///
+/// ```rust
+/// use estring::{Aggregate, EString, SepVec, Product};
+/// let res = EString::from("1*2*3*4")
+///     .parse::<Product<SepVec<i32, '*'>>>()
+///     .unwrap()
+///     .agg();
+/// assert_eq!(res, 24);
+/// ```
+#[derive(Debug, PartialEq, Eq)]
+pub struct Product<T>(pub T);
+
+impl<T> ParseFragment for Product<T>
+where
+    T: ParseFragment,
+{
+    fn parse_frag(es: EString) -> crate::Result<Self> {
+        T::parse_frag(es).map(Self)
+    }
+}
+
+impl<R, T> Aggregate for Product<T>
+where
+    R: std::iter::Product,
+    T: Aggregatable<Item = R>,
+{
+    type Target = R;
+
+    fn agg(self) -> Self::Target {
+        self.0.items().into_iter().product()
+    }
+}
+
+impl<R, T> Aggregatable for Product<T>
+where
+    R: std::iter::Product,
+    T: Aggregatable<Item = R>,
+{
+    type Item = R;
+
+    fn items(self) -> Vec<Self::Item> {
+        vec![self.agg()]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::SepVec;
+
+    use super::*;
+
+    type CommaVec<T> = SepVec<T, ','>;
+    type MulVec<T> = SepVec<T, '*'>;
+
+    #[test]
+    fn should_parse_vec() {
+        let es = EString::from("1,2,3");
+        match es.parse::<Product<CommaVec<i32>>>() {
+            Ok(res) => assert_eq!(res, Product(CommaVec::from(vec![1, 2, 3]))),
+            _ => unreachable!(),
+        }
+    }
+
+    #[test]
+    fn should_aggregate_vector() {
+        let es = EString::from("1,2,3");
+        let expr = es.parse::<Product<CommaVec<i32>>>().unwrap();
+        assert_eq!(expr.agg(), 6);
+    }
+
+    #[test]
+    fn should_aggregate_vector_with_inner_vector() {
+        let es = EString::from("1*2,2,3");
+        let expr = es.parse::<Product<CommaVec<MulVec<i32>>>>().unwrap();
+        assert_eq!(expr.agg(), 12);
+    }
+
+    #[test]
+    fn should_aggregate_vector_with_inner_aggregation() {
+        let es = EString::from("1*2,2,3");
+        let expr = es
+            .parse::<Product<CommaVec<Product<MulVec<i32>>>>>()
+            .unwrap();
+        assert_eq!(expr.agg(), 12);
+    }
+}

src/agg/sum.rs

@@ -0,0 +1,90 @@
+use crate::{Aggregatable, Aggregate, EString, ParseFragment};
+
+/// Aggregate struct, that can sum inner aggregatable [items](Aggregatable::items) if
+/// [``Aggregatable::Item``] implements [``std::iter::Sum``](std::iter::Sum)
+///
+/// # Examples
+///
+/// ```rust
+/// use estring::{Aggregate, EString, SepVec, Sum};
+/// let res = EString::from("1+2+3+4")
+///     .parse::<Sum<SepVec<i32, '+'>>>()
+///     .unwrap()
+///     .agg();
+/// assert_eq!(res, 10);
+/// ```
+#[derive(Debug, PartialEq, Eq)]
+pub struct Sum<T>(pub T);
+
+impl<T> ParseFragment for Sum<T>
+where
+    T: ParseFragment,
+{
+    fn parse_frag(es: EString) -> crate::Result<Self> {
+        T::parse_frag(es).map(Self)
+    }
+}
+
+impl<R, T> Aggregate for Sum<T>
+where
+    R: std::iter::Sum,
+    T: Aggregatable<Item = R>,
+{
+    type Target = R;
+
+    fn agg(self) -> Self::Target {
+        self.0.items().into_iter().sum()
+    }
+}
+
+impl<R, T> Aggregatable for Sum<T>
+where
+    R: std::iter::Sum,
+    T: Aggregatable<Item = R>,
+{
+    type Item = R;
+
+    fn items(self) -> Vec<Self::Item> {
+        vec![self.agg()]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::SepVec;
+
+    use super::*;
+
+    type CommaVec<T> = SepVec<T, ','>;
+    type PlusVec<T> = SepVec<T, '+'>;
+
+    #[test]
+    fn should_parse_vec() {
+        let es = EString::from("1,2,3");
+        match es.parse::<Sum<CommaVec<i32>>>() {
+            Ok(res) => assert_eq!(res, Sum(CommaVec::from(vec![1, 2, 3]))),
+            _ => unreachable!(),
+        }
+    }
+
+    #[test]
+    fn should_aggregate_vector() {
+        let es = EString::from("1,2,3");
+        let expr = es.parse::<Sum<CommaVec<i32>>>().unwrap();
+        assert_eq!(expr.agg(), 6);
+    }
+
+    #[test]
+    fn should_aggregate_vector_with_inner_vector() {
+        let es = EString::from("1+2,2,3");
+        let expr = es.parse::<Sum<CommaVec<PlusVec<i32>>>>().unwrap();
+        assert_eq!(expr.agg(), 8);
+    }
+
+    #[test]
+    fn should_aggregate_vector_with_inner_aggregation() {
+        let es = EString::from("1+2,2,3");
+        let expr = es.parse::<Sum<CommaVec<Sum<PlusVec<i32>>>>>().unwrap();
+        assert_eq!(expr.agg(), 8);
+    }
+}

src/core.rs

@@ -1,54 +1,226 @@
 //! Contains the ``EString`` type, as well as the basic implementation of conversions to
 //! string types
 //!
-#[cfg(any(feature = "number", feature = "bool"))]
-pub mod prim;
-#[cfg(any(feature = "number", feature = "bool"))]
-pub use prim::*;
 
-#[cfg(feature = "vec")]
-pub mod vec;
-#[cfg(feature = "vec")]
-pub use vec::*;
+/// Format this type and wrap into ``EString``.
+///
+/// ``ToEString``’s `to_estring` method is often used implicitly, through ``EString``’s from.
+///
+/// # Examples
+///
+/// Basic implementation of ``ToEString`` on an example ``Point``.
+///
+/// ```rust
+/// use std::fmt::Write;
+/// use estring::{EString, ToEString};
+///
+/// #[derive(Debug, PartialEq)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl ToEString for Point {
+///     fn to_estring(&self) -> EString {
+///         let mut res = String::new();
+///         write!(res, "({},{})", self.x, self.y)
+///             .ok()
+///             .expect("Cannot format Point into EString");
+///         EString(res)
+///     }
+/// }
+///
+/// let point = Point { x: 1, y: 2 };
+/// assert_eq!(point.to_estring(), EString::from("(1,2)"));
+/// ```
+///
+pub trait ToEString {
+    /// Format this type and returns ``EString``.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use estring::{EString, ToEString};
+    ///
+    /// let i = 5;
+    /// let five = EString::from(5);
+    /// assert_eq!(five, i.to_estring());
+    /// ```
+    fn to_estring(&self) -> EString;
+}
 
-#[cfg(feature = "tuple")]
-pub mod tuple;
-#[cfg(feature = "tuple")]
-pub use tuple::*;
-
-#[cfg(feature = "low-level")]
-pub mod low;
-#[cfg(feature = "low-level")]
-pub use low::*;
-
-use crate::ParseError;
-use std::convert::{Infallible, TryFrom};
-
-/// Wrapper under String type.
-#[derive(Debug, Default, PartialEq, Eq, Clone)]
-pub struct EString(pub String);
-
-impl EString {
-    /// Parses inner string by type annotations and returns result.
+/// Parse a value fragment from a ``EString``.
+///
+/// ``ParseFragment``’s `parse_frag` method is often used implicitly, through ``EString``’s parse.
+/// See [parse](EString::parse)’s documentation for examples.
+///
+/// # Examples
+///
+/// Basic implementation of ``ParseFragment`` on an example ``Point``.
+///
+/// ```rust
+/// use estring::{EString, ParseFragment, Reason};
+///
+/// #[derive(Debug, PartialEq)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl ParseFragment for Point {
+///     fn parse_frag(es: EString) -> estring::Result<Self> {
+///         let orig = es.clone();
+///         let (x, y) = es
+///             .trim_matches(|p| p == '(' || p == ')')
+///             .split_once(',')
+///             .ok_or(estring::Error(orig, Reason::Split))?;
+///
+///         let (x, y) = (EString::from(x), EString::from(y));
+///         let x = x.clone().parse::<i32>()
+///             .map_err(|_| estring::Error(x, Reason::Parse))?;
+///         let y = y.clone().parse::<i32>()
+///             .map_err(|_| estring::Error(y, Reason::Parse))?;
+///
+///         Ok(Point { x, y })
+///     }
+/// }
+///
+/// let fragment = EString::from("(1,2)");
+/// let res = Point::parse_frag(fragment).unwrap();
+/// assert_eq!(res, Point { x: 1, y: 2 })
+/// ```
+///
+pub trait ParseFragment: Sized {
+    /// Parses a ``EString`` fragment `es` to return a value of this type.
     ///
     /// # Errors
     ///
-    /// Will return `Err` if estring cannot parse inner fragment
+    /// If parsing is not succeeds, returns ``Error`` inside ``Err`` with original fragment `es`
+    /// and reason ``Reason``.
     ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use estring::{EString, ParseFragment};
+    ///
+    /// let fragment = EString::from("5");
+    /// let res = i32::parse_frag(fragment).unwrap();
+    /// assert_eq!(res, 5);
+    /// ```
+    fn parse_frag(es: EString) -> crate::Result<Self>;
+}
+
+// TODO: add example
+/// Trait to represent structures that can act as aggregators.
+///
+/// The `agg` method works with data that has already been parsed. For this reason, **this trait
+/// should never fail**.
+pub trait Aggregate {
+    /// The resulting type after aggregation.
+    type Target: ?Sized;
+
+    /// Aggregates the value.
+    fn agg(self) -> Self::Target;
+}
+
+// TODO: add example
+/// Trait to represent structures that can iterate values for the aggregator.
+pub trait Aggregatable {
+    /// The type of the elements being iterated over.
+    type Item;
+
+    /// Returns Vec of aggregatable values
+    fn items(self) -> Vec<Self::Item>;
+}
+
+/// Wrapper under ``String`` type.
+///
+/// # Examples
+///
+/// You can create a ``EString`` from a any type that implement ``ToEString`` with ``EString::from``
+///
+/// ```rust
+/// # use estring::EString;
+/// let hello = EString::from("Hello, world");
+/// let num = EString::from("999");
+/// ```
+///
+/// You can use ``ToEString::to_estring`` directly on the type.
+///
+/// ```rust
+/// # use estring::ToEString;
+/// let some_opt = Some(999).to_estring();
+/// let none_opt = None::<i32>.to_estring();
+/// ```
+///
+#[derive(Debug, Default, PartialEq, Eq, Clone)]
+pub struct EString(pub String);
+
+impl std::fmt::Display for EString {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl EString {
+    /// Creates a new empty ``EString``.
+    ///
+    /// This will not allocate any inital buffer.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```rust
+    /// # use estring::EString;
+    /// let s = EString::new();
+    /// ```
+    #[must_use]
     #[inline]
-    pub fn parse<T: TryFrom<EString>>(self) -> Result<T, ParseError> {
-        let orig = self.0.clone();
-        <T as TryFrom<EString>>::try_from(self).map_err(|_| ParseError(orig))
+    pub fn new() -> Self {
+        Self(String::new())
+    }
+
+    /// Parses this inner string into another type.
+    ///
+    /// `parse` can parse into any type that implements the ``ParseFragment`` trait.
+    ///
+    /// # Errors
+    ///
+    /// Will return `Err` if estring cannot parse inner fragment into the desired type.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage
+    ///
+    /// ```rust
+    /// # use estring::{EString, ParseFragment};
+    /// let fragment = EString::from("5");
+    /// let res = i32::parse_frag(fragment);
+    /// assert_eq!(res, Ok(5));
+    /// ```
+    ///
+    /// Failing to parse:
+    ///
+    /// ```rust
+    /// # use estring::{EString, ParseFragment, Error, Reason};
+    /// let fragment = EString::from("j");
+    /// let res = i32::parse_frag(fragment.clone());
+    /// assert_eq!(res, Err(Error(fragment, Reason::Parse)));
+    /// ```
+    #[inline]
+    pub fn parse<T: ParseFragment>(self) -> crate::Result<T> {
+        T::parse_frag(self)
     }
 }
 
 impl<T> From<T> for EString
 where
-    T: std::fmt::Display,
+    T: ToEString,
 {
     #[inline]
     fn from(val: T) -> Self {
-        Self(val.to_string())
+        val.to_estring()
     }
 }
 
@@ -61,21 +233,68 @@ impl std::ops::Deref for EString {
     }
 }
 
-impl TryFrom<EString> for String {
-    type Error = Infallible;
-
+impl ParseFragment for EString {
     #[inline]
-    fn try_from(s: EString) -> Result<Self, Self::Error> {
-        Ok(s.0)
+    fn parse_frag(es: EString) -> crate::Result<Self> {
+        Ok(es)
     }
 }
 
-impl TryFrom<EString> for &'static str {
-    type Error = Infallible;
+#[cfg(feature = "aggs")]
+impl Aggregatable for EString {
+    type Item = Self;
 
     #[inline]
-    fn try_from(s: EString) -> Result<Self, Self::Error> {
-        Ok(Box::leak(s.0.into_boxed_str()))
+    fn items(self) -> Vec<Self::Item> {
+        vec![self]
+    }
+}
+
+impl ParseFragment for String {
+    #[inline]
+    fn parse_frag(es: EString) -> crate::Result<Self> {
+        Ok(es.0)
+    }
+}
+
+impl ToEString for String {
+    #[inline]
+    fn to_estring(&self) -> EString {
+        EString(self.clone())
+    }
+}
+
+#[cfg(feature = "aggs")]
+impl Aggregatable for String {
+    type Item = Self;
+
+    #[inline]
+    fn items(self) -> Vec<Self::Item> {
+        vec![self]
+    }
+}
+
+impl ParseFragment for &'static str {
+    #[inline]
+    fn parse_frag(es: EString) -> crate::Result<Self> {
+        Ok(Box::leak(es.0.into_boxed_str()))
+    }
+}
+
+impl<'a> ToEString for &'a str {
+    #[inline]
+    fn to_estring(&self) -> EString {
+        EString((*self).to_string())
+    }
+}
+
+#[cfg(feature = "aggs")]
+impl<'a> Aggregatable for &'a str {
+    type Item = Self;
+
+    #[inline]
+    fn items(self) -> Vec<Self::Item> {
+        vec![self]
     }
 }
 

src/core/prim.rs

@@ -1,14 +0,0 @@
-//! Contains the implementations to primitive types (number, boolean)
-//!
-//! **NOTE**: Require the enabling of the same-name features
-//!
-
-#[cfg(feature = "bool")]
-mod bool;
-#[cfg(feature = "bool")]
-pub use self::bool::*;
-
-#[cfg(feature = "number")]
-mod number;
-#[cfg(feature = "number")]
-pub use self::number::*;

src/core/prim/number.rs

@@ -1,62 +0,0 @@
-use crate::core::EString;
-use std::convert::TryFrom;
-
-#[doc(hidden)]
-macro_rules! from_env_string_numbers_impl {
-    ($($ty:ty),+$(,)?) => {
-        $(
-            #[cfg(feature = "number")]
-            impl TryFrom<EString> for $ty {
-                type Error = <$ty as std::str::FromStr>::Err;
-
-                #[inline]
-                fn try_from(s: EString) -> Result<Self, Self::Error> {
-                    s.0.parse::<Self>()
-                }
-            }
-        )+
-    };
-}
-
-#[rustfmt::skip]
-from_env_string_numbers_impl![
-    i8, i16, i32, i64, i128, isize,
-    u8, u16, u32, u64, u128, usize,
-    f32, f64
-];
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::ParseError;
-
-    #[test]
-    fn should_parse_number() {
-        let estr = EString::from("-10");
-        match estr.parse::<i32>() {
-            Ok(res) => assert_eq!(res, -10),
-            _ => unreachable!(),
-        };
-    }
-
-    #[test]
-    fn should_parse_float_number() {
-        let estr = EString::from("-0.15");
-        match estr.parse::<f32>() {
-            #[allow(clippy::float_cmp)]
-            Ok(res) => assert_eq!(res, -0.15),
-            _ => unreachable!(),
-        };
-    }
-
-    #[test]
-    fn should_throw_parse_error() {
-        let estr = EString::from("-10");
-        match estr.parse::<u32>() {
-            Err(ParseError(orig)) => {
-                assert_eq!(orig, String::from("-10"));
-            }
-            _ => unreachable!(),
-        };
-    }
-}

src/core/tuple.rs

@@ -1,132 +0,0 @@
-//! Contains the implementations to tuple type
-//!
-//! **NOTE**: Require the enabling of the `tuple` features
-//!
-
-use crate::core::EString;
-use std::convert::TryFrom;
-use std::fmt::Write;
-
-/// The error type for operations interacting with parsing tuples. Possibly returned from
-/// ``EString::parse``
-#[derive(Debug)]
-pub enum Error {
-    /// The specified input string is not split.
-    Split,
-
-    /// The specified substring of the split input string is not parsed
-    Parse(u8),
-}
-
-impl std::fmt::Display for Error {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Error::Split => f.write_str("Cannot split input string"),
-            Error::Parse(n) => write!(f, "Cannot parse {} substring", n),
-        }
-    }
-}
-
-impl std::error::Error for Error {}
-
-/// Wrapper for pair (A, B) tuple to split string by a separator (`S1`).
-///
-/// **NOTE**: Required the enabling of the `tuple` feature.
-///
-/// # Examples
-///
-/// ```rust
-/// use estring::{Pair, EString};
-///
-/// type EqPair<A, B> = Pair<A, '=', B>;
-///
-/// fn main() -> Result<(), estring::ParseError> {
-///     let res = EString::from("one=two=free").parse::<EqPair<&str, &str>>()?;
-///     assert_eq!(res, Pair("one", "two=free"));
-///     Ok(())
-/// }
-/// ```
-///
-#[derive(Debug, PartialEq, Clone)]
-pub struct Pair<A, const S1: char, B>(pub A, pub B);
-
-impl<A, B, const S1: char> From<(A, B)> for Pair<A, S1, B> {
-    #[inline]
-    fn from((a, b): (A, B)) -> Self {
-        Self(a, b)
-    }
-}
-
-impl<A, B, const S1: char> std::fmt::Display for Pair<A, S1, B>
-where
-    A: std::fmt::Display,
-    B: std::fmt::Display,
-{
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        f.write_str(&self.0.to_string())?;
-        f.write_char(S1)?;
-        f.write_str(&self.1.to_string())
-    }
-}
-
-impl<A, const S1: char, B> TryFrom<EString> for Pair<A, S1, B>
-where
-    A: TryFrom<EString>,
-    B: TryFrom<EString>,
-{
-    type Error = Error;
-
-    fn try_from(value: EString) -> Result<Self, Self::Error> {
-        value.split_once(S1).ok_or(Error::Split).and_then(|(a, b)| {
-            let a = A::try_from(EString::from(a)).map_err(|_| Error::Parse(0))?;
-            let b = B::try_from(EString::from(b)).map_err(|_| Error::Parse(1))?;
-            Ok(Self(a, b))
-        })
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    type EqPair<A, B> = Pair<A, '=', B>;
-
-    #[test]
-    fn should_parse_into_pair() {
-        let estr = EString::from("hello=world=hello");
-        match estr.parse::<EqPair<&str, &str>>() {
-            Ok(res) => assert_eq!((res.0, res.1), ("hello", "world=hello")),
-            _ => unreachable!(),
-        };
-    }
-
-    #[test]
-    fn should_parse_rest_as_pair() {
-        let estr = EString::from("hello=world=hello");
-        match estr.parse::<EqPair<&str, EqPair<&str, &str>>>() {
-            Ok(res) => assert_eq!(res, Pair("hello", Pair("world", "hello"))),
-            _ => unreachable!(),
-        };
-    }
-
-    #[cfg(feature = "number")]
-    mod vec {
-        use crate::SepVec;
-
-        use super::*;
-
-        type LineVec<T> = SepVec<T, '\n'>;
-
-        #[test]
-        fn should_parse_vec_of_pairs() {
-            let estr = EString::from(
-                "foo=bar
-hello=bar",
-            );
-            match estr.parse::<LineVec<EqPair<&str, &str>>>() {
-                Ok(res) => assert_eq!(res, SepVec(vec![Pair("foo", "bar"), Pair("hello", "bar"),])),
-                _ => unreachable!(),
-            };
-        }
-    }
-}

src/core/vec.rs

@@ -1,151 +0,0 @@
-//! Contains the implementations to vec type
-//!
-//! **NOTE**: Require the enabling of the `vec` features
-//!
-
-use crate::core::EString;
-use std::convert::TryFrom;
-use std::fmt::Write;
-
-/// Wrapper for ``Vec`` to split string by a separator (`SEP`).
-///
-/// **NOTE**: Required the enabling of the `vec` feature.
-///
-/// # Examples
-///
-/// ```rust
-/// use estring::{SepVec, EString};
-///
-/// type CommaVec<T> = SepVec<T, ','>;
-///
-/// fn main() -> Result<(), estring::ParseError> {
-///     let res = EString::from("1,2,3").parse::<CommaVec<u8>>()?;
-///     assert_eq!(*res, vec![1, 2, 3]);
-///     Ok(())
-/// }
-/// ```
-///
-#[derive(Debug, PartialEq, Clone)]
-pub struct SepVec<T, const SEP: char>(pub Vec<T>);
-
-impl<T, const SEP: char> std::ops::Deref for SepVec<T, SEP> {
-    type Target = Vec<T>;
-
-    #[inline]
-    fn deref(&self) -> &Self::Target {
-        &self.0
-    }
-}
-
-impl<T, const SEP: char> From<Vec<T>> for SepVec<T, SEP> {
-    #[inline]
-    fn from(vec: Vec<T>) -> Self {
-        Self(vec)
-    }
-}
-
-impl<T, const SEP: char> std::fmt::Display for SepVec<T, SEP>
-where
-    T: std::fmt::Display,
-{
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.0.iter().enumerate().try_for_each(|(i, part)| {
-            if i != 0 {
-                f.write_char(SEP)?;
-            }
-
-            f.write_str(&part.to_string())
-        })
-    }
-}
-
-impl<T, const SEP: char> TryFrom<EString> for SepVec<T, SEP>
-where
-    T: TryFrom<EString> + std::fmt::Display,
-{
-    type Error = T::Error;
-
-    fn try_from(value: EString) -> Result<Self, Self::Error> {
-        let inner = value
-            .split(SEP)
-            .map(str::trim)
-            .map(EString::from)
-            .map(T::try_from)
-            .collect::<Result<Vec<_>, _>>()?;
-        Ok(Self(inner))
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    const COMMA: char = ',';
-    const SEMI: char = ';';
-
-    type CommaVec<T> = SepVec<T, COMMA>;
-    type SemiVec<T> = SepVec<T, SEMI>;
-
-    #[test]
-    fn should_parse_into_vec() {
-        let estr = EString::from("a,b,c,d,e");
-        match estr.parse::<CommaVec<&str>>() {
-            Ok(res) => assert_eq!(*res, vec!["a", "b", "c", "d", "e"]),
-            _ => unreachable!(),
-        };
-    }
-
-    #[test]
-    fn should_trim_identations_before_parsing() {
-        let input = "
-a , b, c,
-d,e";
-        let estr = EString::from(input);
-        match estr.parse::<CommaVec<&str>>() {
-            Ok(res) => assert_eq!(*res, vec!["a", "b", "c", "d", "e"]),
-            _ => unreachable!(),
-        };
-    }
-
-    #[test]
-    fn should_parse_into_vector_of_vectors() {
-        let estr = EString::from("a,b; c,d,e; f,g");
-        match estr.parse::<SemiVec<CommaVec<&str>>>() {
-            Ok(res) => assert_eq!(
-                res,
-                SemiVec::from(vec![
-                    CommaVec::from(vec!["a", "b"]),
-                    CommaVec::from(vec!["c", "d", "e"]),
-                    CommaVec::from(vec!["f", "g"])
-                ])
-            ),
-            _ => unreachable!(),
-        };
-    }
-
-    #[cfg(feature = "number")]
-    mod numbers {
-        use super::*;
-        use crate::ParseError;
-
-        #[test]
-        fn should_parse_into_num_vec() {
-            let estr = EString::from("1,2,3,4,5");
-            match estr.parse::<CommaVec<i32>>() {
-                Ok(res) => assert_eq!(*res, vec![1, 2, 3, 4, 5]),
-                _ => unreachable!(),
-            };
-        }
-
-        #[test]
-        fn should_throw_parse_vec_error() {
-            let estr = EString::from("1,2,3,4,5");
-            match estr.parse::<SemiVec<i32>>() {
-                Err(ParseError(orig)) => {
-                    assert_eq!(orig, String::from("1,2,3,4,5"));
-                }
-                _ => unreachable!(),
-            };
-        }
-    }
-}

src/error.rs

@@ -1,16 +1,31 @@
-/// Failed to parse the specified string.
-#[derive(Debug)]
-pub struct ParseError(pub String);
+use crate::core::EString;
 
-impl std::fmt::Display for ParseError {
+/// The error type for operations interacting with ``EString``’s fragments.
+#[derive(Debug, PartialEq, Eq)]
+pub struct Error(pub EString, pub Reason);
+
+/// The reason for the failure to parse.
+#[derive(Debug, PartialEq, Eq)]
+pub enum Reason {
+    /// Cannot split fragment
+    Split,
+    /// Cannot parse fragment
+    Parse,
+}
+
+impl std::fmt::Display for Error {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, r#"Failed to parse: "{}""#, self.0)
+        write!(
+            f,
+            r#"Failed to parse "{:?}" with reason {:?}"#,
+            self.0, self.1
+        )
     }
 }
 
-impl std::error::Error for ParseError {}
+impl std::error::Error for Error {}
 
-impl std::ops::Deref for ParseError {
+impl std::ops::Deref for Error {
     type Target = String;
 
     fn deref(&self) -> &Self::Target {

src/lib.rs

@@ -7,7 +7,23 @@
 //!
 //! [enve]: https://github.com/pleshevskiy/enve
 //!
-//! ## Getting started
+//! ## Usage
+//!
+//! Basic
+//!
+//! ```rust
+//! use estring::EString;
+//!
+//! fn main() -> estring::Result<()> {
+//!     let res: i32 = EString::from("10").parse()?;
+//!     assert_eq!(res, 10);
+//!     Ok(())
+//! }
+//! ```
+//!
+//! You can use predefined structs like ``SepVec`` if you enable `structs` feature.
+//!
+//! Note: You can use custom types as annotations! Just implement ``ParseFragment``!
 //!
 //! ```rust
 //! use estring::{SepVec, EString};
@@ -15,7 +31,7 @@
 //! type PlusVec<T> = SepVec<T, '+'>;
 //! type MulVec<T> = SepVec<T, '*'>;
 //!
-//! fn main() -> Result<(), estring::ParseError> {
+//! fn main() -> estring::Result<()> {
 //!     let res = EString::from("10+5*2+3")
 //!         .parse::<PlusVec<MulVec<f32>>>()?
 //!         .iter()
@@ -27,12 +43,88 @@
 //! }
 //! ```
 //!
+//! You can also use predefined aggregators if you enable `aggs` feature.
+//!
+//! ```rust
+//! use estring::{Aggregate, EString, Product, SepVec, Sum};
+//!
+//! type PlusVec<T> = SepVec<T, '+'>;
+//! type MulVec<T> = SepVec<T, '*'>;
+//!
+//! fn main() -> estring::Result<()> {
+//!     let res = EString::from("10+5*2+3")
+//!         .parse::<Sum<PlusVec<Product<MulVec<f32>>>>>()?
+//!         .agg();
+//!
+//!     assert_eq!(res, 23.0);
+//!     Ok(())
+//! }
+//! ```
+//!
+//! ---
+//!
+//! For more details, see [examples].
+//!
+//! [examples]: https://github.com/pleshevskiy/estring/tree/main/examples
+//!
 #![deny(clippy::pedantic)]
 #![allow(clippy::module_name_repetitions)]
 #![warn(missing_docs)]
 
-pub mod core;
 mod error;
+pub use error::{Error, Reason};
+/// The type returned by parser methods.
+///
+/// # Examples
+///
+/// ```rust
+/// use estring::{EString, ParseFragment, Reason};
+///
+/// #[derive(Debug, PartialEq)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl ParseFragment for Point {
+///     fn parse_frag(es: EString) -> estring::Result<Self> {
+///         let orig = es.clone();
+///         let (x, y) = es
+///             .trim_matches(|p| p == '(' || p == ')')
+///             .split_once(',')
+///             .ok_or(estring::Error(orig, Reason::Split))?;
+///
+///         let (x, y) = (EString::from(x), EString::from(y));
+///         let x = x.clone().parse::<i32>()
+///             .map_err(|_| estring::Error(x, Reason::Parse))?;
+///         let y = y.clone().parse::<i32>()
+///             .map_err(|_| estring::Error(y, Reason::Parse))?;
+///
+///         Ok(Point { x, y })
+///     }
+/// }
+///
+/// let fragment = EString::from("(1,2)");
+/// let res = Point::parse_frag(fragment).unwrap();
+/// assert_eq!(res, Point { x: 1, y: 2 })
+/// ```
+pub type Result<T> = ::std::result::Result<T, Error>;
+
+pub mod core;
+pub mod std;
+
+#[cfg(feature = "aggs")]
+pub mod agg;
+#[cfg(feature = "aggs")]
+pub use agg::*;
+
+#[cfg(feature = "low-level")]
+pub mod low;
+#[cfg(feature = "low-level")]
+pub use low::*;
+#[cfg(feature = "structs")]
+pub mod structs;
+#[cfg(feature = "structs")]
+pub use structs::*;
 
 pub use crate::core::*;
-pub use crate::error::ParseError;

src/low/trim.rs

@@ -1,9 +1,4 @@
-use crate::core::EString;
-use std::convert::TryFrom;
-
-//===========================================================================//
-// TRIM                                                                      //
-//===========================================================================//
+use crate::core::{EString, ParseFragment, ToEString};
 
 /// Wrapper that allow to trim substring before continue
 ///
@@ -14,7 +9,7 @@ use std::convert::TryFrom;
 /// ```rust
 /// use estring::{EString, Trim};
 ///
-/// fn main() -> Result<(), estring::ParseError> {
+/// fn main() -> estring::Result<()> {
 ///     let res = EString::from(" 99 ").parse::<Trim<i32>>()?;
 ///     assert_eq!(res, Trim(99));
 ///     Ok(())
@@ -38,16 +33,21 @@ impl<T: std::fmt::Display> std::fmt::Display for Trim<T> {
     }
 }
 
-impl<T> TryFrom<EString> for Trim<T>
+impl<T> ParseFragment for Trim<T>
 where
-    T: TryFrom<EString>,
+    T: ParseFragment,
 {
-    type Error = ();
+    fn parse_frag(value: EString) -> crate::Result<Self> {
+        T::parse_frag(EString::from(value.trim())).map(Trim)
+    }
+}
 
-    fn try_from(value: EString) -> Result<Self, Self::Error> {
-        T::try_from(EString::from(value.trim()))
-            .map(Trim)
-            .map_err(|_| ())
+impl<T> ToEString for Trim<T>
+where
+    T: ToEString,
+{
+    fn to_estring(&self) -> EString {
+        self.0.to_estring()
     }
 }
 
@@ -65,7 +65,6 @@ mod tests {
         }
     }
 
-    #[cfg(feature = "number")]
     #[test]
     fn should_trim_and_convert_to_number() {
         let estr = EString::from("    999   ");

src/std.rs

@@ -0,0 +1,6 @@
+//! Contains implementations for standard types (`bool`, numbers, `Option`, etc.)
+//!
+
+mod bool;
+mod number;
+mod option;

src/std/bool.rs

@@ -1,23 +1,37 @@
-use crate::core::EString;
-use std::convert::TryFrom;
-
-impl TryFrom<EString> for bool {
-    type Error = ();
+use crate::core::{EString, ParseFragment, ToEString};
+use crate::error::{Error, Reason};
 
+impl ParseFragment for bool {
     #[inline]
-    fn try_from(s: EString) -> Result<Self, Self::Error> {
+    fn parse_frag(s: EString) -> crate::Result<Self> {
         match s.to_lowercase().as_str() {
             "true" | "t" | "yes" | "y" | "on" | "1" => Ok(true),
             "false" | "f" | "no" | "n" | "off" | "0" | "" => Ok(false),
-            _ => Err(()),
+            _ => Err(Error(s, Reason::Parse)),
         }
     }
 }
 
+impl ToEString for bool {
+    #[inline]
+    fn to_estring(&self) -> EString {
+        EString(self.to_string())
+    }
+}
+
+#[cfg(feature = "aggs")]
+impl crate::core::Aggregatable for bool {
+    type Item = Self;
+
+    #[inline]
+    fn items(self) -> Vec<Self::Item> {
+        vec![self]
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::ParseError;
 
     #[test]
     fn should_parse_bool_variable() {
@@ -48,10 +62,17 @@ mod tests {
     fn should_throw_parse_error() {
         let estr = EString::from("something");
         match estr.parse::<bool>() {
-            Err(ParseError(orig)) => {
-                assert_eq!(orig, String::from("something"));
+            Err(crate::Error(orig, reason)) => {
+                assert_eq!(orig, EString::from("something"));
+                assert_eq!(reason, crate::Reason::Parse);
             }
             _ => unreachable!(),
         };
     }
+
+    #[test]
+    fn should_format_bool() {
+        assert_eq!(true.to_estring(), EString(String::from("true")));
+        assert_eq!(false.to_estring(), EString(String::from("false")));
+    }
 }

src/std/number.rs

@@ -0,0 +1,83 @@
+use crate::core::{EString, ParseFragment, ToEString};
+use crate::error::{Error, Reason};
+
+#[doc(hidden)]
+macro_rules! from_env_string_numbers_impl {
+    ($($ty:ty),+$(,)?) => {
+        $(
+            impl ParseFragment for $ty {
+                #[inline]
+                fn parse_frag(s: EString) -> crate::Result<Self> {
+                    s.0.parse::<Self>().map_err(|_| Error(s, Reason::Parse))
+                }
+            }
+
+            impl ToEString for $ty {
+                #[inline]
+                fn to_estring(&self) -> EString {
+                    EString(self.to_string())
+                }
+            }
+
+            #[cfg(feature = "aggs")]
+            impl crate::core::Aggregatable for $ty {
+                type Item = Self;
+
+                #[inline]
+                fn items(self) -> Vec<Self::Item> {
+                    vec![self]
+                }
+            }
+        )+
+    };
+}
+
+#[rustfmt::skip]
+from_env_string_numbers_impl![
+    i8, i16, i32, i64, i128, isize,
+    u8, u16, u32, u64, u128, usize,
+    f32, f64
+];
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn should_parse_number() {
+        let estr = EString::from("-10");
+        match estr.parse::<i32>() {
+            Ok(res) => assert_eq!(res, -10),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_parse_float_number() {
+        let estr = EString::from("-0.15");
+        match estr.parse::<f32>() {
+            #[allow(clippy::float_cmp)]
+            Ok(res) => assert_eq!(res, -0.15),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_throw_parse_error() {
+        let estr = EString::from("-10");
+        match estr.parse::<u32>() {
+            Err(Error(orig, reason)) => {
+                assert_eq!(orig, EString::from("-10"));
+                assert_eq!(reason, Reason::Parse);
+            }
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_format_number() {
+        assert_eq!((-1).to_estring(), EString(String::from("-1")));
+        assert_eq!(10.to_estring(), EString(String::from("10")));
+        assert_eq!(1.1.to_estring(), EString(String::from("1.1")));
+    }
+}

src/std/option.rs

@@ -0,0 +1,77 @@
+use crate::core::{EString, ParseFragment, ToEString};
+
+impl<T> ToEString for Option<T>
+where
+    T: ToEString,
+{
+    fn to_estring(&self) -> EString {
+        match self {
+            Some(inner) => inner.to_estring(),
+            None => EString::new(),
+        }
+    }
+}
+
+impl<T> ParseFragment for Option<T>
+where
+    T: ParseFragment,
+{
+    fn parse_frag(es: EString) -> crate::Result<Self> {
+        if es.is_empty() {
+            Ok(None)
+        } else {
+            es.parse().map(Some)
+        }
+    }
+}
+
+#[cfg(feature = "aggs")]
+impl<T> crate::core::Aggregatable for Option<T>
+where
+    T: crate::core::Aggregatable,
+{
+    type Item = T::Item;
+
+    fn items(self) -> Vec<Self::Item> {
+        self.map(T::items).unwrap_or_default()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::structs::Pair;
+
+    #[test]
+    fn should_parse_empty_string_as_none() {
+        let estr = EString::new();
+        match estr.parse::<Option<i32>>() {
+            Ok(res) => assert_eq!(res, None),
+            _ => unreachable!(),
+        }
+    }
+
+    #[test]
+    fn should_parse_number_as_some() {
+        let estr = EString::from("99");
+        match estr.parse::<Option<i32>>() {
+            Ok(res) => assert_eq!(res, Some(99)),
+            _ => unreachable!(),
+        }
+    }
+
+    #[test]
+    fn should_parse_pair() {
+        let estr = EString::from("1+2");
+        match estr.parse::<Option<Pair<i32, '+', i32>>>() {
+            Ok(res) => assert_eq!(res, Some(Pair(1, 2))),
+            _ => unreachable!(),
+        }
+    }
+
+    #[test]
+    fn should_format_option() {
+        assert_eq!(None::<i32>.to_estring(), EString::new());
+        assert_eq!(Some(99).to_estring(), EString(String::from("99")));
+    }
+}

src/structs.rs

@@ -0,0 +1,12 @@
+//! Contains the predefined types (``SepVec``, ``Pair``, etc.)
+//!
+//! **NOTE**: Require the enabling the `structs` feature.
+//!
+
+mod pair;
+mod sep_vec;
+mod trio;
+
+pub use pair::*;
+pub use sep_vec::*;
+pub use trio::*;

src/structs/pair.rs

@@ -0,0 +1,125 @@
+//! Contains the implementations to pair tuple type
+//!
+
+use crate::core::{EString, ParseFragment, ToEString};
+use crate::{Error, Reason};
+use std::fmt::Write;
+
+/// Wrapper for pair (A, B) tuple to split string by a separator (`S1`).
+///
+/// **NOTE**: Required the enabling of the `structs` feature.
+///
+/// # Examples
+///
+/// ```rust
+/// use estring::{Pair, EString};
+///
+/// type EqPair<A, B> = Pair<A, '=', B>;
+///
+/// fn main() -> estring::Result<()> {
+///     let res = EString::from("one=two=free").parse::<EqPair<&str, &str>>()?;
+///     assert_eq!(res, Pair("one", "two=free"));
+///     Ok(())
+/// }
+/// ```
+///
+#[derive(Debug, PartialEq, Clone)]
+pub struct Pair<A, const S1: char, B>(pub A, pub B);
+
+impl<A, B, const S1: char> From<(A, B)> for Pair<A, S1, B> {
+    #[inline]
+    fn from((a, b): (A, B)) -> Self {
+        Self(a, b)
+    }
+}
+
+impl<A, B, const S1: char> std::fmt::Display for Pair<A, S1, B>
+where
+    A: std::fmt::Display,
+    B: std::fmt::Display,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}{}{}", self.0, S1, self.1)
+    }
+}
+
+impl<A, B, const S1: char> ToEString for Pair<A, S1, B>
+where
+    A: ToEString,
+    B: ToEString,
+{
+    fn to_estring(&self) -> EString {
+        let mut res = String::new();
+        write!(res, "{}{}{}", self.0.to_estring(), S1, self.1.to_estring())
+            .ok()
+            .expect("Cannot parse Pair to EString");
+        EString(res)
+    }
+}
+
+impl<A, B, const S1: char> ParseFragment for Pair<A, S1, B>
+where
+    A: ParseFragment,
+    B: ParseFragment,
+{
+    fn parse_frag(value: EString) -> crate::Result<Self> {
+        value
+            .clone()
+            .split_once(S1)
+            .ok_or(Error(value, Reason::Split))
+            .and_then(|(a, b)| {
+                let (a, b) = (EString::from(a), EString::from(b));
+                let a = A::parse_frag(a.clone()).map_err(|_| Error(a, Reason::Parse))?;
+                let b = B::parse_frag(b.clone()).map_err(|_| Error(b, Reason::Parse))?;
+                Ok(Self(a, b))
+            })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::structs::SepVec;
+
+    type EqPair<A, B> = Pair<A, '=', B>;
+
+    #[test]
+    fn should_parse_into_pair() {
+        let estr = EString::from("hello=world=hello");
+        match estr.parse::<EqPair<&str, &str>>() {
+            Ok(res) => assert_eq!((res.0, res.1), ("hello", "world=hello")),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_parse_rest_as_pair() {
+        let estr = EString::from("hello=world=hello");
+        match estr.parse::<EqPair<&str, EqPair<&str, &str>>>() {
+            Ok(res) => assert_eq!(res, Pair("hello", Pair("world", "hello"))),
+            _ => unreachable!(),
+        };
+    }
+
+    type LineVec<T> = SepVec<T, '\n'>;
+
+    #[test]
+    fn should_parse_vec_of_pairs() {
+        let estr = EString::from(
+            "foo=bar
+hello=bar",
+        );
+        match estr.parse::<LineVec<EqPair<&str, &str>>>() {
+            Ok(res) => assert_eq!(res, SepVec(vec![Pair("foo", "bar"), Pair("hello", "bar"),])),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_format_pair() {
+        let pair = Pair::<_, '+', _>(1, 2);
+        assert_eq!(pair.to_estring(), EString(String::from("1+2")));
+        let pair_in_pair = Pair::<_, '=', _>(3, pair);
+        assert_eq!(pair_in_pair.to_estring(), EString(String::from("3=1+2")));
+    }
+}

src/structs/sep_vec.rs

@@ -0,0 +1,198 @@
+//! Contains the implementations to vec type
+//!
+
+use crate::core::{EString, ParseFragment, ToEString};
+use std::fmt::Write;
+
+/// Wrapper for ``Vec`` to split string by a separator (`SEP`).
+///
+/// **NOTE**: Required the enabling of the `structs` feature.
+///
+/// # Examples
+///
+/// ```rust
+/// use estring::{SepVec, EString};
+///
+/// type CommaVec<T> = SepVec<T, ','>;
+///
+/// fn main() -> estring::Result<()> {
+///     let res = EString::from("1,2,3").parse::<CommaVec<u8>>()?;
+///     assert_eq!(*res, vec![1, 2, 3]);
+///     Ok(())
+/// }
+/// ```
+///
+#[derive(Debug, PartialEq, Clone)]
+pub struct SepVec<T, const SEP: char>(pub Vec<T>);
+
+impl<T, const SEP: char> std::ops::Deref for SepVec<T, SEP> {
+    type Target = Vec<T>;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T, const SEP: char> From<Vec<T>> for SepVec<T, SEP> {
+    #[inline]
+    fn from(vec: Vec<T>) -> Self {
+        Self(vec)
+    }
+}
+
+impl<T, const SEP: char> std::fmt::Display for SepVec<T, SEP>
+where
+    T: std::fmt::Display,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.iter().enumerate().try_for_each(|(i, part)| {
+            if i != 0 {
+                f.write_char(SEP)?;
+            }
+
+            write!(f, "{}", part)
+        })
+    }
+}
+
+impl<T, const SEP: char> ToEString for SepVec<T, SEP>
+where
+    T: ToEString,
+{
+    fn to_estring(&self) -> EString {
+        self.0
+            .iter()
+            .enumerate()
+            .try_fold(String::new(), |mut res, (i, part)| {
+                if i != 0 {
+                    res.write_char(SEP).ok()?;
+                }
+
+                write!(res, "{}", part.to_estring()).ok()?;
+                Some(res)
+            })
+            .map(EString)
+            .expect("Cannot format SepVec ${self.0} to EString")
+    }
+}
+
+impl<T, const SEP: char> ParseFragment for SepVec<T, SEP>
+where
+    T: ParseFragment,
+{
+    fn parse_frag(value: EString) -> crate::Result<Self> {
+        let inner = value
+            .split(SEP)
+            .map(str::trim)
+            .map(EString::from)
+            .map(T::parse_frag)
+            .collect::<crate::Result<Vec<_>>>()?;
+        Ok(Self(inner))
+    }
+}
+
+#[cfg(feature = "aggs")]
+impl<T, const SEP: char> crate::core::Aggregatable for SepVec<T, SEP>
+where
+    T: crate::core::Aggregatable,
+{
+    type Item = T::Item;
+
+    fn items(self) -> Vec<Self::Item> {
+        self.0.into_iter().flat_map(T::items).collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::Aggregatable;
+    use crate::Pair;
+    use crate::{Error, Reason};
+
+    type CommaVec<T> = SepVec<T, ','>;
+    type SemiVec<T> = SepVec<T, ';'>;
+
+    #[test]
+    fn should_parse_into_vec() {
+        let estr = EString::from("a,b,c,d,e");
+        match estr.parse::<CommaVec<&str>>() {
+            Ok(res) => assert_eq!(*res, vec!["a", "b", "c", "d", "e"]),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_trim_identations_before_parsing() {
+        let input = "
+a , b, c,
+d,e";
+        let estr = EString::from(input);
+        match estr.parse::<CommaVec<&str>>() {
+            Ok(res) => assert_eq!(*res, vec!["a", "b", "c", "d", "e"]),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_parse_into_vector_of_vectors() {
+        let estr = EString::from("a,b; c,d,e; f,g");
+        match estr.parse::<SemiVec<CommaVec<&str>>>() {
+            Ok(res) => assert_eq!(
+                res,
+                SemiVec::from(vec![
+                    CommaVec::from(vec!["a", "b"]),
+                    CommaVec::from(vec!["c", "d", "e"]),
+                    CommaVec::from(vec!["f", "g"])
+                ])
+            ),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_parse_into_num_vec() {
+        let estr = EString::from("1,2,3,4,5");
+        match estr.parse::<CommaVec<i32>>() {
+            Ok(res) => assert_eq!(*res, vec![1, 2, 3, 4, 5]),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_throw_parse_vec_error() {
+        let estr = EString::from("1,2,3,4,5");
+        match estr.parse::<SemiVec<i32>>() {
+            Err(Error(orig, reason)) => {
+                assert_eq!(orig, EString::from("1,2,3,4,5"));
+                assert_eq!(reason, Reason::Parse);
+            }
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_format_vec() {
+        type PlusPair<T> = Pair<T, '+', T>;
+
+        let vec = SepVec::<_, ','>::from(vec![1, 2, 3]);
+        assert_eq!(vec.to_estring(), EString(String::from("1,2,3")));
+        let vec = SepVec::<_, ','>::from(vec![PlusPair::from((1, 2)), PlusPair::from((3, 4))]);
+        assert_eq!(vec.to_estring(), EString(String::from("1+2,3+4")));
+    }
+
+    #[test]
+    fn should_returns_aggregatable_items() {
+        let estr = EString::from("1,2,3,4,5");
+        let res = estr.parse::<CommaVec<i32>>().unwrap();
+        assert_eq!(res.items(), vec![1, 2, 3, 4, 5]);
+    }
+
+    #[test]
+    fn should_returns_flatten_aggregatable_items() {
+        let estr = EString::from("1,2; 3,4,5; 6,7");
+        let res = estr.parse::<SemiVec<CommaVec<i32>>>().unwrap();
+        assert_eq!(res.items(), vec![1, 2, 3, 4, 5, 6, 7]);
+    }
+}

src/structs/trio.rs

@@ -0,0 +1,132 @@
+//! Contains the implementations to parse triple-tuple type
+//!
+
+use super::Pair;
+use crate::core::{EString, ParseFragment, ToEString};
+use std::fmt::Write;
+
+/// Wrapper for trio (A, B, C) tuple to split string by separators (`S1` and `S2`).
+///
+/// **NOTE**: Required the enabling of the `structs` feature.
+///
+/// # Examples
+///
+/// ```rust
+/// use estring::{Trio, EString};
+///
+/// fn main() -> estring::Result<()> {
+///     let res = EString::from("one+two=free").parse::<Trio<&str, '+', &str, '=', &str>>()?;
+///     assert_eq!(res, Trio("one", "two", "free"));
+///     Ok(())
+/// }
+/// ```
+///
+#[derive(Debug, PartialEq, Clone)]
+pub struct Trio<A, const S1: char, B, const S2: char, C>(pub A, pub B, pub C);
+
+impl<A, B, C, const S1: char, const S2: char> From<(A, B, C)> for Trio<A, S1, B, S2, C> {
+    #[inline]
+    fn from((a, b, c): (A, B, C)) -> Self {
+        Self(a, b, c)
+    }
+}
+
+impl<A, B, C, const S1: char, const S2: char> std::fmt::Display for Trio<A, S1, B, S2, C>
+where
+    A: std::fmt::Display,
+    B: std::fmt::Display,
+    C: std::fmt::Display,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&self.0.to_string())?;
+        f.write_char(S1)?;
+        f.write_str(&self.1.to_string())?;
+        f.write_char(S2)?;
+        f.write_str(&self.2.to_string())
+    }
+}
+
+impl<A, B, C, const S1: char, const S2: char> ToEString for Trio<A, S1, B, S2, C>
+where
+    A: ToEString,
+    B: ToEString,
+    C: ToEString,
+{
+    fn to_estring(&self) -> EString {
+        let mut res = String::new();
+        write!(
+            res,
+            "{}{}{}{}{}",
+            self.0.to_estring(),
+            S1,
+            self.1.to_estring(),
+            S2,
+            self.2.to_estring()
+        )
+        .ok()
+        .expect("Cannot parse Pair to EString");
+        EString(res)
+    }
+}
+
+impl<A, const S1: char, B, const S2: char, C> ParseFragment for Trio<A, S1, B, S2, C>
+where
+    A: ParseFragment,
+    B: ParseFragment,
+    C: ParseFragment,
+{
+    fn parse_frag(value: EString) -> crate::Result<Self> {
+        Pair::<A, S1, EString>::parse_frag(value).and_then(|Pair(a, rest)| {
+            Pair::<B, S2, C>::parse_frag(rest).map(|Pair(b, c)| Self(a, b, c))
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    type EqTrio<A, B, C> = Trio<A, '=', B, '=', C>;
+
+    #[test]
+    fn should_parse_into_trio() {
+        let estr = EString::from("hello=world=hello");
+        match estr.parse::<EqTrio<&str, &str, &str>>() {
+            Ok(res) => assert_eq!((res.0, res.1, res.2), ("hello", "world", "hello")),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_parse_into_trio_with_alternate_delims() {
+        let estr = EString::from("hello-world^hello");
+        match estr.parse::<Trio<&str, '-', &str, '^', &str>>() {
+            Ok(res) => assert_eq!((res.0, res.1, res.2), ("hello", "world", "hello")),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_parse_rest_as_trio() {
+        let estr = EString::from("hello=world=hello=world=hello");
+        match estr.parse::<EqTrio<&str, &str, EqTrio<&str, &str, &str>>>() {
+            Ok(res) => assert_eq!(res, Trio("hello", "world", Trio("hello", "world", "hello"))),
+            _ => unreachable!(),
+        };
+    }
+
+    #[test]
+    fn should_format_trio() {
+        let trio = Trio::<_, '+', _, '-', _>::from(("foo", "baz", "bar"));
+        assert_eq!(
+            trio.clone().to_estring(),
+            EString(String::from("foo+baz-bar"))
+        );
+
+        let trio_in_trio = Trio::<_, '*', _, '=', _>::from(("foo", "baz", trio));
+        assert_eq!(
+            trio_in_trio.clone().to_estring(),
+            EString(String::from("foo*baz=foo+baz-bar"))
+        );
+    }
+}