druid 0.6.0

Data-oriented Rust UI design toolkit.
Documentation 
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// Copyright 2020 The xi-editor Authors.
//
// 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 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.

//! Miscellaneous utility functions.

use std::collections::HashMap;
use std::hash::Hash;
use std::mem;

/// Fast path for equal type extend + drain.
pub trait ExtendDrain {
    /// Extend the collection by draining the entries from `source`.
    ///
    /// This function may swap the underlying memory locations,
    /// so keep that in mind if one of the collections has a large allocation
    /// and it should keep that allocation.
    fn extend_drain(&mut self, source: &mut Self);
}

impl<K, V> ExtendDrain for HashMap<K, V>
where
    K: Eq + Hash + Copy,
    V: Copy,
{
    // Benchmarking this vs just extend+drain with a 10k entry map.
    //
    // running 2 tests
    // test bench_extend       ... bench:       1,971 ns/iter (+/- 566)
    // test bench_extend_drain ... bench:           0 ns/iter (+/- 0)
    fn extend_drain(&mut self, source: &mut Self) {
        if !source.is_empty() {
            if self.is_empty() {
                // If the target is empty we can just swap the pointers.
                mem::swap(self, source);
            } else {
                // Otherwise we need to fall back to regular extend-drain.
                self.extend(source.drain());
            }
        }
    }
}