chore: cleanup unused imports

Cargo.lock

@@ -1,6 +1,7 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+version = 3
+
 [[package]]
 name = "estring"
-version = "0.1.2"
-
+version = "0.3.0"

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "estring"
 description = "A simple way to parse a string using type annotations"
-version = "0.1.2"
+version = "0.3.0"
 edition = "2021"
 authors = ["Dmitriy Pleshevskiy <dmitriy@ideascup.me>"]
 readme = "README.md"
@@ -28,7 +28,7 @@ maintenance = { status = "actively-developed" }
 
 [[example]]
 name = "calc"
-required-features = ["structs"]
+required-features = ["structs", "aggs"]
 
 [[example]]
 name = "dotenv"

README.md

@@ -7,7 +7,7 @@
 
 ```toml
 [dependencies]
-estring = "0.1"
+estring = "0.3"
 ```
 
 A simple way to parse a string using type annotations.
@@ -24,6 +24,23 @@ For more details, see [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};
 
@@ -42,8 +59,23 @@ fn main() -> estring::Result<()> {
 }
 ```
 
-You can use custom types as annotations! Just implement
-`estring::ParseFragment`!
+You can also use predefined aggregators if you enable the `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(())
+}
+```
 
 ## Contact Us
 

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() -> 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(())

src/agg.rs

@@ -1,2 +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

@@ -2,11 +2,51 @@
 //! string types
 //!
 
-// TODO: add more info and examples.
-/// Format a value fragment into a ``EString``.
-pub trait FormatFragment {
+/// 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``.
-    fn fmt_frag(&self) -> 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;
 }
 
 /// Parse a value fragment from a ``EString``.
@@ -70,11 +110,77 @@ pub trait ParseFragment: Sized {
     fn parse_frag(es: EString) -> crate::Result<Self>;
 }
 
-/// Wrapper under String type.
+// 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 new() -> Self {
+        Self(String::new())
+    }
+
     /// Parses this inner string into another type.
     ///
     /// `parse` can parse into any type that implements the ``ParseFragment`` trait.
@@ -110,11 +216,11 @@ impl EString {
 
 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()
     }
 }
 
@@ -129,22 +235,66 @@ impl std::ops::Deref for EString {
 
 impl ParseFragment for EString {
     #[inline]
-    fn parse_frag(value: EString) -> crate::Result<Self> {
-        Ok(value)
+    fn parse_frag(es: EString) -> crate::Result<Self> {
+        Ok(es)
+    }
+}
+
+#[cfg(feature = "aggs")]
+impl Aggregatable for EString {
+    type Item = Self;
+
+    #[inline]
+    fn items(self) -> Vec<Self::Item> {
+        vec![self]
     }
 }
 
 impl ParseFragment for String {
     #[inline]
-    fn parse_frag(s: EString) -> crate::Result<Self> {
-        Ok(s.0)
+    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(s: EString) -> crate::Result<Self> {
-        Ok(Box::leak(s.0.into_boxed_str()))
+    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/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};
@@ -27,6 +43,30 @@
 //! }
 //! ```
 //!
+//! 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)]

src/low/trim.rs

@@ -1,4 +1,4 @@
-use crate::{core::EString, ParseFragment};
+use crate::core::{EString, ParseFragment, ToEString};
 
 /// Wrapper that allow to trim substring before continue
 ///
@@ -42,6 +42,15 @@ where
     }
 }
 
+impl<T> ToEString for Trim<T>
+where
+    T: ToEString,
+{
+    fn to_estring(&self) -> EString {
+        self.0.to_estring()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/std/bool.rs

@@ -1,4 +1,4 @@
-use crate::core::{EString, ParseFragment};
+use crate::core::{EString, ParseFragment, ToEString};
 use crate::error::{Error, Reason};
 
 impl ParseFragment for bool {
@@ -12,6 +12,23 @@ impl ParseFragment for bool {
     }
 }
 
+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::*;
@@ -52,4 +69,10 @@ mod tests {
             _ => 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

@@ -1,4 +1,4 @@
-use crate::core::{EString, ParseFragment};
+use crate::core::{EString, ParseFragment, ToEString};
 use crate::error::{Error, Reason};
 
 #[doc(hidden)]
@@ -11,6 +11,23 @@ macro_rules! from_env_string_numbers_impl {
                     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]
+                }
+            }
         )+
     };
 }
@@ -56,4 +73,11 @@ mod tests {
             _ => 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

@@ -1,4 +1,16 @@
-use crate::core::{EString, ParseFragment};
+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
@@ -13,6 +25,18 @@ where
     }
 }
 
+#[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::*;
@@ -20,7 +44,7 @@ mod tests {
 
     #[test]
     fn should_parse_empty_string_as_none() {
-        let estr = EString::from("");
+        let estr = EString::new();
         match estr.parse::<Option<i32>>() {
             Ok(res) => assert_eq!(res, None),
             _ => unreachable!(),
@@ -44,4 +68,10 @@ mod tests {
             _ => 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/pair.rs

@@ -1,7 +1,7 @@
 //! Contains the implementations to pair tuple type
 //!
 
-use crate::core::{EString, ParseFragment};
+use crate::core::{EString, ParseFragment, ToEString};
 use crate::{Error, Reason};
 use std::fmt::Write;
 
@@ -39,13 +39,25 @@ where
     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())
+        write!(f, "{}{}{}", self.0, S1, self.1)
     }
 }
 
-impl<A, const S1: char, B> ParseFragment for Pair<A, S1, B>
+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,
@@ -102,4 +114,12 @@ 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

@@ -1,7 +1,7 @@
 //! Contains the implementations to vec type
 //!
 
-use crate::core::{EString, ParseFragment};
+use crate::core::{EString, ParseFragment, ToEString};
 use std::fmt::Write;
 
 /// Wrapper for ``Vec`` to split string by a separator (`SEP`).
@@ -51,11 +51,32 @@ where
                 f.write_char(SEP)?;
             }
 
-            f.write_str(&part.to_string())
+            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,
@@ -71,16 +92,27 @@ where
     }
 }
 
+#[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};
 
-    const COMMA: char = ',';
-    const SEMI: char = ';';
-
-    type CommaVec<T> = SepVec<T, COMMA>;
-    type SemiVec<T> = SepVec<T, SEMI>;
+    type CommaVec<T> = SepVec<T, ','>;
+    type SemiVec<T> = SepVec<T, ';'>;
 
     #[test]
     fn should_parse_into_vec() {
@@ -139,4 +171,28 @@ d,e";
             _ => 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

@@ -2,7 +2,7 @@
 //!
 
 use super::Pair;
-use crate::core::{EString, ParseFragment};
+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`).
@@ -46,6 +46,29 @@ where
     }
 }
 
+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,
@@ -91,4 +114,19 @@ mod tests {
             _ => 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"))
+        );
+    }
 }