问题描述

几个 Linq.Enumerable 函数采用 IEqualityComparer<T>.是否有一个方便的包装类来适应 delegate(T,T)=>bool 来实现 IEqualityComparer<T>?编写一个很容易(如果您忽略了定义正确哈希码的问题)，但我想知道是否有开箱即用的解决方案.

Several Linq.Enumerable functions take an IEqualityComparer<T>. Is there a convenient wrapper class that adapts a delegate(T,T)=>bool to implement IEqualityComparer<T>? It's easy enough to write one (if your ignore problems with defining a correct hashcode), but I'd like to know if there is an out-of-the-box solution.

具体来说，我想对 Dictionary 进行设置操作，只使用 Keys 来定义成员资格(同时根据不同的规则保留值).

Specifically, I want to do set operations on Dictionarys, using only the Keys to define membership (while retaining the values according to different rules).

推荐答案

通常情况下，我会通过在答案上评论 @Sam 来解决这个问题(我已经对原始帖子进行了一些编辑，以便在没有改变行为.)

Ordinarily, I'd get this resolved by commenting @Sam on the answer (I've done some editing on the original post to clean it up a bit without altering the behavior.)

以下是我的 @Sam 的回答的即兴演奏, 对默认散列策略进行了 [IMNSHO] 关键修复:-

The following is my riff of @Sam's answer, with a [IMNSHO] critical fix to the default hashing policy:-

class FuncEqualityComparer<T> : IEqualityComparer<T>
{
    readonly Func<T, T, bool> _comparer;
    readonly Func<T, int> _hash;

    public FuncEqualityComparer( Func<T, T, bool> comparer )
        : this( comparer, t => 0 ) // NB Cannot assume anything about how e.g., t.GetHashCode() interacts with the comparer's behavior
    {
    }

    public FuncEqualityComparer( Func<T, T, bool> comparer, Func<T, int> hash )
    {
        _comparer = comparer;
        _hash = hash;
    }

    public bool Equals( T x, T y )
    {
        return _comparer( x, y );
    }

    public int GetHashCode( T obj )
    {
        return _hash( obj );
    }
}

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