Storing a lambda in a variable in c#

Question

I'm writing some code in C# to call a method that takes a callback. The method being called takes a callback as an optional parameter.

In this case I don't really need a callback for production purposes, but I'd like to put a Debug.Log in while I'm developing so I'm throwing in a lambda to log the results.

(Note that I fully understand this isn't necessary, I can just do the log in the called method, but this question is more about me learning how to do things in c# than practicality)

WebUtilities.instance.PushExperimentDataToApi(experimentType, formData, result => Debug.Log(result));

This works fine, but I'd like to pull that debug log out into a variable and pass in the variable instead. In other languages that I'm used to (dynamic) I could do something like:

let debug = string => console.log(string)
myClass.myMethod(arg1, arg2, debug)

And from looking around it seems like I may be able to accomplish the same thing with tuples, but I haven't quite figured out how.

Is there a way to do this? Again, I know this isn't necessary or practical in this case, I'm just using this as an example to better understand the language while building a project.

Pavel Anikhouski · Accepted Answer · 2020-05-20 07:42:28Z

3

You can use Action<T> delegate for that

Action<string> debug = s => Debug.WriteLine(s);

And invoke it like debug("test"); or debug.Invoke("test");. You can also it pass to myMethod to invoke inside it.

myMethod in this case should accept an Action<string> debug parameter

void myMethod(object arg1, object arg2, Action<string> debug)
{
    ...
    debug("test");
}

edited May 20, 2020 at 7:42

answered May 19, 2020 at 21:52

Pavel Anikhouski

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Ondrej Tucny · Accepted Answer · 2020-05-19 21:52:23Z

1

You can achieve this with delegates, and in particular the Action<T>:

Action<string> debug = s => Console.WriteLine(s);

and then the following will work as you expect:

myClass.myMethod(arg1, arg2, debug)

where myMethod is declared as follows:

public void myMethod(SomeType arg1, SomeType arg2, Action<string> debug) 
{
    … 
    debug("something");
    …
}

answered May 19, 2020 at 21:52

Ondrej Tucny

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1 Comment

Chris Schmitz Over a year ago

Thanks for the quick reply. It's appreciated!

IV. · Accepted Answer · 2020-05-19 22:40:45Z

1

Is this the kind of thing you're after?

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Calling method with anonymous lambda.");
        do
        {
            Foo((string name, object data) =>
            {
                Console.WriteLine(name + "=" + data);
            });
        } while (Console.ReadKey().Key != ConsoleKey.Escape);

        do
        {
            Console.WriteLine("Calling method with null logger.");
            Foo();
        } while (Console.ReadKey().Key != ConsoleKey.Escape);


        Console.WriteLine("Calling method with delegate.");
        do
        {
            Foo(Logger);
        } while (Console.ReadKey().Key != ConsoleKey.Escape);
    }

    // Example exercising the Action<T1, T2, ...> delegate per accepted answer
    static void Foo(Action<string, object> logger = null)
    {
        int data = _random.Next(1, 100);
        logger?.Invoke("Random Number", data);
    }

    static void Logger(string name, object data)
    {
        Console.WriteLine(name + ":" + data);
    }

    // Sample data generator
    static readonly Random _random = new Random();
}

Where console output might be:

Calling method anonymous lambda.
Random Number=24
Random Number=76
Random Number=11
Calling method with null logger.
Calling method with null logger.
Calling method with null logger.
Calling method with null logger.
Calling method with delegate.
Random Number:37
Random Number:74
Random Number:25
Random Number:82

edited May 19, 2020 at 22:40

answered May 19, 2020 at 22:09

IV.

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2 Comments

Chris Schmitz Over a year ago

Hmm, not completely. I was looking for an equivalent to an implementation that I was already familiar with in a different language, but this is still helpful to look :) There are some structures and implementations in here that I haven't seen yet in c#. Thanks :)

IV. Over a year ago

I'm happy to see that while I was typing furiously you got your solution in a more simple fashion and it's good that you marked the one you did as an answer. Really, this is just 3 variations of that. As others pointed out, the key to this sample is the use of Action<string, object> as the argument to Foo.

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