Constrangeiter

This small utility crate provides const-evaluable iterators for ranges using the new range API.

Problem it solves

Current ranges in rust, either with the old API (core::ops::Range) or the new API (core::range::Range) do not implement const IntoIterator nor the produced iterators implement const Iterator. That makes them impossible to evaluate in const contexts.

For that reason, we made a ConstIntoIterator trait implemented for the ranges (normal, inclusive, and only starting), that is naturally const and whose produced iterators are const-evaluable as well.

Usage

use libutils::constrangeiter::ConstIntoIterator;

const {
    for index in (0..6).const_into_iter() {
        // ..
    }
}

The method .const_into_iter() -> impl const Iterator must be explicitly called (it is not called by the rust machinery) and it converts the range into a constant iterator.

When to use it

This is useful in contexts like constant iteration, and it is used in parts of libutils-array.

For example, if we want to drop some elements in an array-like storage, we first want to iterate over them and drop each one by one. That process would be const iff Type: [const] Destruct, but if range iteration is never const, we don't get to ever make it const even if the type has a constant drop implementation.

This crate requires the #![feature(new_range)] attribute, as const ConstIntoIterator has not been implemented for the old range types.