CreateDelegate Derived classes must provide an implementation

Question

When calling creating a compiled expressiong I'm trying to call CreateDelegate on the resultant compiled delegate, but am geeting a NotSupportedException, with the explanation being: Derived classes must provide an implementation. How do I create the delegate for a compiled method?

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.