字典用Func键为重点 [英] Dictionary with Func as key

问题描述

我想知道，如果这是关键的一个字典一个理智的选择吗？我想要做的是使用一个表达式作为字典的关键，是这样的：

I am wondering if this is a sane choice of key for a dictionary? What I want to do is use an expression as the key in a dictionary, something like:

    var map3 = new Dictionary<Func<int, bool>, int>();
    map3.Add((x) => x % 2 == 0, 1);
    map3.Add((x) => x % 10 == 0, 2);
    // ...

    var key = map3.Keys.SingleOrDefault(f => f(2));
    // key = (x) => x % 2
    // map3[key] = 1

这个想法是这是一比有大的if-else或switch语句更清洁的方式。

The idea being this is a cleaner way than having big if-else or switch statements.

这是否有道理？它是否行得通呢？是否有一个更简单的方法？

Does this make sense? Will it work? Is there an simpler way?

推荐答案

没有，C＃构造每当一个lambda使用，所以你不会成为一个新的委托实例能够使用它作为一个一致的密钥。例如：

No, C# constructs a new delegate instance whenever a lambda is used so you wouldn't be able to use it as a consistent key. Example:

        Func<int, int> f = x => x*x + 1;
        Func<int, int> g = x => x*x + 1;
        Console.WriteLine(f.Equals(g)); // prints False

这会然后进行使用的尴尬作为字典的键，除非你有一些其他的方式来，总是得到相同的实例

This would then make usage awkward as a dictionary key unless you had some other way to always obtain the same instance.

编辑：

埃里克利珀的回答的here 表示该编译器的允许的检测lambda表达式是相同的（尽管它通常没有）。无论哪种方式，一个lambda /委托使得一个键一个糟糕的选择。

Eric Lippert's answer here indicates that the compiler is allowed to detect the lambdas are the same (although it typically does not). Either way a lambda/delegate makes a poor choice for a key.

这篇关于字典用Func键为重点的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！