C#•16mo ago

❔ Delegates

c#
namespace MWE
{
    internal class Program
    {
        static int add(int a, int b) { 
            return a + b;
        }
        static void Main(string[] args)
        {
            Delegate esum = add;
            Console.WriteLine(esum(4, 6));
        }
    }
}

c#
namespace MWE
{
    internal class Program
    {
        static int add(int a, int b) { 
            return a + b;
        }
        static void Main(string[] args)
        {
            Delegate esum = add;
            Console.WriteLine(esum(4, 6));
        }
    }
}

This code doesn't compile and I don't understand the issue. What Am I doing wrong?

29 Replies

Thinker•16mo ago

Use Func<int, int, int> instead Delegate is just the base type for all delegate types (like Func), but it's not actually invokable

MODiX•16mo ago

thinker227#5176

REPL Result: Success

static int Add(int a, int b)
{
    return a + b;
}

Func<int, int, int> esum = Add;
Console.WriteLine(esum(4, 6));

static int Add(int a, int b)
{
    return a + b;
}

Func<int, int, int> esum = Add;
Console.WriteLine(esum(4, 6));

Console Output

Compile: 642.841ms | Execution: 43.745ms | React with ❌ to remove this embed.

júlio•16mo ago

So I should use it like I would a pointer to base class? For polymorhpism stuff For example, take in a Delegate as parameters and cast to the actual function type?

Thinker•16mo ago

Delegate on its own is generally pretty useless I don't think I've ever seen a situation where you'd have to use Delegate as a base class, even though you can

júlio•16mo ago

Maybe for dynamic stuff, but yes I can see it not being very usefull

Thinker•16mo ago

Also, you can actually just use var here and let the compiler infer the type of the delegate for you.

var esum = Add;
Console.WriteLine(esum(4, 6));

var esum = Add;
Console.WriteLine(esum(4, 6));

júlio•16mo ago

Yes. I come from C++ and now I have to learn C# for work realated things, so I'm kinda trying out aspects of the language I appreciate the explanation

Thinker•16mo ago

I think in C++ you have some really long and obscure method pointer syntax...?

júlio•16mo ago

there are some wrappers around function pointers std;:function is a common one, tho it has a bit of overhead you still have to tell it the type of the function ther isnt really a way to have a Delegate like c# since the functions don't come from a common object

Thinker•16mo ago

You can actually use raw method pointers in C#, but for 99% of cases you should use Func and Action, and for the other 0.9% you can create your own delegate types.

júlio•16mo ago

I'll look into that :)

júlio•16mo ago

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/delegates/using-delegates?source=recommendations

Using Delegates - C# Programming Guide

Learn how to use delegates. Delegates are an object-oriented, type safe, and secure type that safely encapsulates a method.

júlio•16mo ago

One thing I didnt quite understand I though that in order to be able to use a function as a delegate, I would have to mark it like so public delegate void Del(string message); But the compiler allows me to not do that declaration "The following example declares a delegate named Del that can encapsulate a method that takes a string as an argument and returns void" Okay I think I get it That is the syntax for a function pointer I though that it was related to the function itself I wanted to point to my bad So this means I have 2 different ways of doing thins

public delegate int Calculation(int a, int b);
static int add(int a, int b) { 
    return a + b;
}

static int subtract(int a, int b) {  
    return a - b; 
}
static void Main(string[] args)
{
    Calculation c = add;            // #1
    Func<int, int, int> esum = add; // #2
    Console.WriteLine(esum(4, 6));
}

public delegate int Calculation(int a, int b);
static int add(int a, int b) { 
    return a + b;
}

static int subtract(int a, int b) {  
    return a - b; 
}
static void Main(string[] args)
{
    Calculation c = add;            // #1
    Func<int, int, int> esum = add; // #2
    Console.WriteLine(esum(4, 6));
}

Weird the syntax hightlight doesnt seem to be recognising c#

Anton•16mo ago

$codegif

MODiX•16mo ago

https://cdn.discordapp.com/attachments/364492811489509376/892176158312001586/code.gif

júlio•16mo ago

That did it, thanks

Anton•16mo ago

Func is declared the same way you declared Calculation I think, it just happens to also allow a few generic parameters, which you could allow too, in principle delegate types are a useful abstraction sometimea don't hesitate to use them

júlio•16mo ago

Is it common for primitive types to be alias of the System.(...) equivalent? For example, double and System.Double, double here would be an alias to System.Double, correct?

Anton•16mo ago

all of them have their corresponding regular types

júlio•16mo ago

So I can assume that everything comes from the System

Anton•16mo ago

I think so

júlio•16mo ago

Is anything bellow the System? Or is it the base of everything? I think Java follows a similar dynamic For objects atleast

Anton•16mo ago

here, the names don't always correspond to their primitive names tho like float is Single, int is Int32, etc.

júlio•16mo ago

https://stackoverflow.com/questions/436211/is-everything-in-net-an-object

Stack Overflow

Is everything in .NET an object?

Please help us settle the controversy of "Nearly" everything is an object (an answer to Stack Overflow question As a novice, is there anything I should beware of before learning C#?). I thought tha...

júlio•16mo ago

The top comment also covers the question I asked

Thinker•16mo ago

System in C# is just a namespace, and namespaces don't really mean anything other than as a way to organize code. If you wanna be pedantic, there is technically the global:: namespace, but that's only used for very niche scenarios.

júlio•16mo ago

A namespace yes, my bad :)

Accord•16mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Delegates