Added helper traits for indexing

Author: LucaCappelletti94

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Support for tuple conversions with proper error handling and type safety
 - `TupleRow<Idx>` and `TupleRowMut<Idx>` traits for indexing rows in tuples of tuples
 - `FirstTupleRow` and `LastTupleRow` convenience traits for accessing the first and last rows in tuples of tuples
+- `FirstTupleIndex` and `LastTupleIndex` convenience traits for accessing the first and last elements in tuples
 
 ## [0.1.0] - 2025-12-05
 

Cargo.lock

@@ -49,6 +49,8 @@ The library provides several traits for working with tuples:
 - [`PairTuple`](https://docs.rs/tuplities-len/latest/tuplities_len/trait.PairTuple.html): A marker trait implemented for two-element tuples `(T1, T2)` with `TupleLen<Len = U2>`.
 - [`TupleIndex<Idx>`](https://docs.rs/tuplities-index/latest/tuplities_index/trait.TupleIndex.html): Provides an [`index()`](https://docs.rs/tuplities-index/latest/tuplities_index/trait.TupleIndex.html#tymethod.index) method to access the element at the specified index [`typenum`](https://docs.rs/typenum/latest/typenum/)'s `Idx` of the tuple.
 - [`TupleIndexMut<Idx>`](https://docs.rs/tuplities-index/latest/tuplities_index/trait.TupleIndexMut.html): Provides an [`index_mut()`](https://docs.rs/tuplities-index/latest/tuplities_index/trait.TupleIndexMut.html#tymethod.index_mut) method to access a mutable reference to the element at the specified index [`typenum`](https://docs.rs/typenum/latest/typenum/)'s `Idx` of the tuple.
+- [`FirstTupleIndex`](https://docs.rs/tuplities-index/latest/tuplities_index/trait.FirstTupleIndex.html): A convenience trait providing a [`first_tuple_index()`](https://docs.rs/tuplities-index/latest/tuplities_index/trait.FirstTupleIndex.html#tymethod.first_tuple_index) method to access the first element of a tuple.
+- [`LastTupleIndex`](https://docs.rs/tuplities-index/latest/tuplities_index/trait.LastTupleIndex.html): A convenience trait providing a [`last_tuple_index()`](https://docs.rs/tuplities-index/latest/tuplities_index/trait.LastTupleIndex.html#tymethod.last_tuple_index) method to access the last element of a tuple.
 - [`TupleRow<Idx>`](https://docs.rs/tuplities-row/latest/tuplities_row/trait.TupleRow.html): Provides a [`tuple_row()`](https://docs.rs/tuplities-row/latest/tuplities_row/trait.TupleRow.html#tymethod.tuple_row) method to access elements at the specified index across all tuples in a tuple of tuples (row-wise indexing).
 - [`TupleRowMut<Idx>`](https://docs.rs/tuplities-row/latest/tuplities_row/trait.TupleRowMut.html): Provides a [`tuple_row_mut()`](https://docs.rs/tuplities-row/latest/tuplities_row/trait.TupleRowMut.html#tymethod.tuple_row_mut) method to access mutable elements at the specified index across all tuples in a tuple of tuples (mutable row-wise indexing).
 - [`FirstTupleRow`](https://docs.rs/tuplities-row/latest/tuplities_row/trait.FirstTupleRow.html): A convenience trait providing a [`first_tuple_row()`](https://docs.rs/tuplities-row/latest/tuplities_row/trait.FirstTupleRow.html#tymethod.first_tuple_row) method to access the first element of each tuple in a tuple of tuples.

README.md

@@ -15,6 +15,7 @@ homepage.workspace = true
 [dependencies]
 typenum = { workspace = true }
 tuplities-derive = { workspace = true }
+tuplities-len = { workspace = true }
 
 [features]
 default = []

tuplities-index/Cargo.toml

@@ -5,6 +5,8 @@
 
 #![no_std]
 
+use tuplities_len::TupleLen;
+
 /// A trait for indexing into tuples at compile-time known positions.
 ///
 /// This trait allows accessing elements at specific indices `Idx`
@@ -23,7 +25,7 @@
 ///
 /// Part of the [`tuplities`](https://docs.rs/tuplities/latest/tuplities/) crate.
 #[tuplities_derive::impl_tuple_index]
-pub trait TupleIndex<Idx: typenum::Unsigned> {
+pub trait TupleIndex<Idx: typenum::Unsigned>: TupleLen {
     /// The type of the element at index `Idx`.
     type Type;
 
@@ -53,3 +55,65 @@ pub trait TupleIndexMut<Idx: typenum::Unsigned>: TupleIndex<Idx> {
     /// Returns a mutable reference to the element at index `Idx`.
     fn tuple_index_mut(&mut self) -> &mut Self::Type;
 }
+
+/// A convenience trait for accessing the first element (index 0) in tuples.
+///
+/// This trait is automatically implemented for any tuple that implements `TupleIndex<U0>`.
+///
+/// # Examples
+///
+/// ```
+/// use tuplities_index::FirstTupleIndex;
+///
+/// let tuple = (1, "hello", 3.14);
+/// let first = tuple.first_tuple_index();
+/// assert_eq!(*first, 1);
+/// ```
+///
+/// Part of the [`tuplities`](https://docs.rs/tuplities/latest/tuplities/) crate.
+pub trait FirstTupleIndex: TupleIndex<typenum::U0> {
+    /// Returns a reference to the first element in the tuple.
+    fn first_tuple_index(&self) -> &Self::Type {
+        self.tuple_index()
+    }
+}
+
+impl<T: TupleIndex<typenum::U0>> FirstTupleIndex for T {}
+
+/// A convenience trait for accessing the last element in tuples.
+///
+/// This trait is automatically implemented for any tuple that implements `TupleIndex<LastIndex>`
+/// where `LastIndex` is calculated as `TupleLen::Len - 1`.
+///
+/// # Examples
+///
+/// ```
+/// use tuplities_index::LastTupleIndex;
+///
+/// let tuple = (1, "hello", 3.14);
+/// let last = tuple.last_tuple_index();
+/// assert_eq!(*last, 3.14);
+/// ```
+///
+/// Part of the [`tuplities`](https://docs.rs/tuplities/latest/tuplities/) crate.
+pub trait LastTupleIndex:
+    TupleIndex<
+        <<Self as TupleLen>::Len as core::ops::Sub<typenum::U1>>::Output,
+        Len: core::ops::Sub<typenum::U1, Output: typenum::Unsigned>,
+    >
+{
+    /// Returns a reference to the last element in the tuple.
+    fn last_tuple_index(&self) -> &Self::Type;
+}
+
+impl<T> LastTupleIndex for T
+where
+    T: TupleIndex<
+            <<T as TupleLen>::Len as core::ops::Sub<typenum::U1>>::Output,
+            Len: core::ops::Sub<typenum::U1, Output: typenum::Unsigned>,
+        >,
+{
+    fn last_tuple_index(&self) -> &Self::Type {
+        self.tuple_index()
+    }
+}

tuplities-index/src/lib.rs

@@ -10,7 +10,7 @@ pub mod prelude {
     pub use tuplities_eq::TupleEq;
     pub use tuplities_from::{TupleFrom, TupleInto};
     pub use tuplities_hash::TupleHash;
-    pub use tuplities_index::{TupleIndex, TupleIndexMut};
+    pub use tuplities_index::{FirstTupleIndex, LastTupleIndex, TupleIndex, TupleIndexMut};
     pub use tuplities_insert::TupleInsert;
     pub use tuplities_len::{PairTuple, SingletonTuple, TupleLen, UnitTuple};
     pub use tuplities_mut::TupleMut;