问题描述

这是我直到今天才注意到的.显然，.NET 实现的常用元组类(Tuple<T>、Tuple<T1、T2> 等)会导致 值类型 执行基于等式的操作时.

This is something I had not noticed until today. Apparently, the .NET implementation of the much used tuple classes (Tuple<T>, Tuple<T1, T2> etc) causes boxing penalties for value types when equality based operations are performed.

以下是该类在框架中的实现方式(来自 ILSpy):

Here is how the class is kind of implemented in the framework (source via ILSpy):

public class Tuple<T1, T2> : IStructuralEquatable 
{
    public T1 Item1 { get; private set; }
    public T2 Item2 { get; private set; }

    public Tuple(T1 item1, T2 item2)
    {
        this.Item1 = item1;
        this.Item2 = item2;
    }

    public override bool Equals(object obj)
    {
        return this.Equals(obj, EqualityComparer<object>.Default);
    }

    public override int GetHashCode()
    {
        return this.GetHashCode(EqualityComparer<object>.Default);
    }

    public bool Equals(object obj, IEqualityComparer comparer)
    {
        if (obj == null)
        {
            return false;
        }

        var tuple = obj as Tuple<T1, T2>;
        return tuple != null 
            && comparer.Equals(this.Item1, tuple.Item1) 
            && comparer.Equals(this.Item2, tuple.Item2);
    }

    public int GetHashCode(IEqualityComparer comparer)
    {
        int h1 = comparer.GetHashCode(this.Item1);
        int h2 = comparer.GetHashCode(this.Item2);

        return (h1 << 5) + h1 ^ h2;
    }
}

我看到的问题是它会导致两阶段装箱-拆箱，例如 Equals 调用，一个，在 comparer.Equals 将项目装箱，两个，EqualityComparer