C#lambda表达式和IComparer

Question

我使用lambda表达式来排序和搜索C#中的数组.我不想在我的类中实现IComparer接口,因为我需要对多个成员字段进行排序和搜索.

class Widget
{
    public int foo;

    public void Bar()
    {
        Widget[] widgets;

        Array.Sort(widgets, (a, b) => a.foo.CompareTo(b.foo));

        Widget x = new Widget();
        x.foo = 5;
        int index = Array.BinarySearch(widgets, x,
                                       (a, b) => a.foo.CompareTo(b.foo));
    }
}

虽然排序工作正常,但二进制搜索会产生编译错误无法将lambda表达式转换为类型'System.Collections.IComparer <Widget>',因为它不是委托类型.由于某种原因,Sort对IComparer和Comparison都有重载,但BinarySearch只支持IComparer.经过一些研究,我发现ComparisonComparer<T>将比较转换为IComparer 的笨重:

public class ComparisonComparer<T> : IComparer<T>
{
    private readonly Comparison<T> comparison;

    public ComparisonComparer(Comparison<T> comparison)
    {
        this.comparison = comparison;
    }

    int IComparer<T>.Compare(T x, T y)
    {
        return comparison(x, y);
    }
}

这允许二进制搜索如下工作:

int index = Array.BinarySearch(
  widgets,
  x,
  new ComparisonComparer<Widget>((a, b) => a.foo.CompareTo(b.foo)));

呸.有更干净的方式吗？

Answer 1

嗯,一个选择是创建类似的东西ProjectionComparer.我在MiscUtil中有一个版本- 它基本上是IComparer<T>从投影创建的.

所以你的例子是:

int index = Array.BinarySearch(widgets, x,
                               ProjectionComparer<Widget>.Create(x => x.foo));

或者你可以实现自己的扩展方法T[]来做同样的事情:

public static int BinarySearchBy<TSource, TKey>(
    this TSource[] array,
    TSource value,
    Func<TSource, TKey> keySelector)
{
    return Array.BinarySearch(array, value,
                              ProjectionComparer.Create(array, keySelector));
}

Answer 2

你可以用我的ValueComparer<T>班级:

int index = Array.BinarySearch(
    widgets, x,
    new ValueComparer<Widget>(x => x.Foo)
);

您可以通过传递多个lambda表达式来比较多个属性.