#![no_std]

extern crate alloc;

mod copypasted_impl;
pub use copypasted_impl::DrainFilter;

/// An extension trait to make `drain_filter` accessible, implemented for `Vec`.
pub trait VecExt<T> {
    /// Creates an iterator which uses a closure to determine if an element should be removed.
    ///
    /// If the closure returns true, then the element is removed and yielded.
    /// If the closure returns false, the element will remain in the vector and will not be yielded
    /// by the iterator.
    ///
    /// Using this method is equivalent to the following code:
    ///
    /// ```
    /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
    /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
    /// let mut i = 0;
    /// while i < vec.len() {
    ///     if some_predicate(&mut vec[i]) {
    ///         let val = vec.remove(i);
    ///         // your code here
    ///     } else {
    ///         i += 1;
    ///     }
    /// }
    ///
    /// # assert_eq!(vec, vec![1, 4, 5]);
    /// ```
    ///
    /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
    /// because it can backshift the elements of the array in bulk.
    ///
    /// Note that `drain_filter` also lets you mutate every element in the filter closure,
    /// regardless of whether you choose to keep or remove it.
    ///
    /// # Examples
    ///
    /// Splitting an array into evens and odds, reusing the original allocation:
    ///
    /// ```
    /// use drain_filter_polyfill::VecExt;
    /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
    ///
    /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
    /// let odds = numbers;
    ///
    /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
    /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
    /// ```
    fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
    where
        F: FnMut(&mut T) -> bool;
}