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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License in the LICENSE file at the
// root of this repository, or online at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Iterator utilities.

use std::iter::{self, Chain, Once};

/// Extension methods for iterators.
pub trait IteratorExt
where
    Self: Iterator + Sized,
{
    /// Chains a single `item` onto the end of this iterator.
    ///
    /// Equivalent to `self.chain(iter::once(item))`.
    fn chain_one(self, item: Self::Item) -> Chain<Self, Once<Self::Item>> {
        self.chain(iter::once(item))
    }

    /// Reports whether all the elements of the iterator are the same.
    ///
    /// This condition is trivally true for iterators with zero or one elements.
    fn all_equal(mut self) -> bool
    where
        Self::Item: PartialEq,
    {
        match self.next() {
            None => true,
            Some(v1) => self.all(|v2| v1 == v2),
        }
    }
}

impl<I> IteratorExt for I where I: Iterator {}

#[cfg(test)]
mod tests {
    use crate::iter::IteratorExt;

    #[test]
    fn test_all_equal() {
        assert!(([] as [i64; 0]).iter().all_equal());
        assert!([1].iter().all_equal());
        assert!([1, 1].iter().all_equal());
        assert!(![1, 2].iter().all_equal());
    }
}