c# - CreateDelegate 派生类必须提供实现

Question

在调用创建编译表达式时，我试图在生成的编译委托上调用 CreateDelegate，但遇到 NotSupportedException，解释是：派生类必须提供实现。如何为已编译的方法创建委托？

public delegate int AddOne(int input);

void Main()
{
    var input = Expression.Parameter(typeof(int));
    var add = Expression.Add(input,Expression.Constant(1));
    var lambda = Expression.Lambda(typeof(AddOne),add,input);
    var compiled = (AddOne)lambda.Compile();
    compiled.Method.CreateDelegate(typeof(AddOne));
}

Answer 1

You don't need to call CreateDelegate. Casting the result from lambda.Compile to AddOne was all you needed.

Observe:

public delegate int AddOne(int input);

public int Test(AddOne f)
{
   return f(1);
}

void Main()
{
    var input = Expression.Parameter(typeof(int));
    var add = Expression.Add(input,Expression.Constant(1));
    var lambda = Expression.Lambda(typeof(AddOne),add,input);
    var compiled = (AddOne)lambda.Compile();
    Console.WriteLine(Test(compiled)); // 2
}

You can successfully call the Test method, which accepts a delegate of type AddOne.