Creating multicast delegate--failure

Question

I have a multicast delegate question.

This is based on some code in C# In A Nutshell Version 5.

using System;
using System.Collections;
using System.Collections.Generic;

public delegate int Transformer(int x);

class MainClass
{
    static int Square(int x) { return x * x; }
    static int Cube(int x) { return x * x * x; }

    static void Main()
    {
        Transformer t, q, multi;
        t = Square;
        q = Cube;

        multi = t + q;
        for (int i = 1; i < 5; i++)
            Console.WriteLine(multi(i));
    }
}

The output is from Cube alone. Why does the addition fail?

Wrong operator, you meant to use t(i) + q(i). The C# compiler makes hay of your current code by calling Delegate.Combine(). Giving you a new delegate object that calls both targets, one after another. The result is whatever is returned by the last target. — Hans Passant
– Hans Passant, Commented Nov 20, 2014 at 16:06

Servy · Accepted Answer · 2014-11-20 15:44:57Z

1

First the Square method runs and then the Cube method runs for each value. The return value of multi() is the return value of last method in the invocation list, so that's why you see only the value of Cubes.

The addition does not faill it works as expected. You can verify this by putting a Console.WriteLine inside of the Square method.

edited Nov 20, 2014 at 15:44

Servy

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answered Nov 20, 2014 at 15:41

Selman Genç

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1 Comment

Servy Over a year ago

@Ron That's almost certainly not the proper design here. You should simply apply a collection of delegates, rather than a single delegate with multiple associated methods.

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