Dictionary with Func as key

Question

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 m         


        

Answer 1

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

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

Edit:

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.