How can I create an open Delegate from a struct's instance method?

Question

I have a struct with a private method that I\'d like to invoke. Since I plan to do this in a performance critical section, I\'d like to cache a delegate to perform the actio

Answer 1

You're using this overload of CreateDelegate:

Creates a delegate of the specified type to represent the specified static method.

SomeMethod is not a static method.

Use an overload that allows to specify a target object:

A target = new A();

Func f = (Func)Delegate.CreateDelegate(
    typeof(Func),
    target,
    typeof(A).GetMethod(
        "SomeMethod",
        BindingFlags.Instance | BindingFlags.NonPublic));

This means you need to create a delegate for each instance of A though. You cannot reuse the same delegate for different instances.

The best solution is probably to construct a Lambda Expression using LINQ Expression Trees:

var p = Expression.Parameter(typeof(A), "arg");
var lambda = Expression.Lambda>(
    Expression.Call(
        p,
        typeof(A).GetMethod(
            "SomeMethod",
            BindingFlags.Instance | BindingFlags.NonPublic)),
    p);

Func f = lambda.Compile();