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You can certainly change it. But should you? (lemmy.ml)

submitted 8 months ago by [email protected] to c/programmer_humor

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[–] [email protected] 8 points 8 months ago (10 children)

You can do that in memory safe languages too. Kotlin extension functions, for example.

[–] RonSijm 16 points 8 months ago* (last edited 8 months ago) (9 children)

Extension functions are not the same at all. Extension functions are syntactic sugar. For example if you have an extension function like

public static class ObjectExtension
{
    public static void DoSomething(this object input) { }
}

You can call that function on an object by doing object.DoSomething() - Yes. But underneath it's the same as doing ObjectExtension.DoSomething(object)

That function does not actually become part of the object, and you can't use it to override existing functions

A closer example of how to do something similar in a memory safe language would be - in C# - using something like Castle DynamicProxy - where through a lot of black magic - you can create a DynamicProxy and fool the CLR into thinking it's talking to an object, while it's actually talking to a DynamicProxy instead. And so then you can actually intercept invocations to existing methods and overrule them

Generally overruling existing functions at runtime is not that easy

[–] [email protected] 2 points 8 months ago (1 children)

That actually sounds pretty cool

Sometimes what I'd like to be able to do is treat part of an app as a core and the rest like user provided scripts, but written and evaluated in the host language and not running an embedded scripting language like lua with all the extra burden.

E.g. you have an image editor and you want the user to be able to write native functions to process the image. Or you have a game engine and you want to inject new game code from the user without the engine being a compiler or the game logic being bundled scripts.

[–] RonSijm 4 points 8 months ago

You'd probably use a different approach for that. Like you'd make your program dynamically load all the .dlls in a "plugins" folder -

Then you'd provide some plugin interface for the users to create plugins, for example:

public interface IImageEditorPlugin
{
    public void BeforeImageEdit(int[,] imageData);
    public void AfterImageEdit(int[,] imageData);
}

And then you can load plugin classes from all the dlls with dependency injection, and execute them though something like this:

public class ImageEditor(IEnumerable<IImageEditorPlugin> plugins)
{
    public void EditImage(int[,] imageData)
    {
        foreach (var imageEditorPlugin in plugins)
        {
            imageEditorPlugin.BeforeImageEdit(imageData);
            // Do internal image edit function
            imageEditorPlugin.AfterImageEdit(imageData);
        }
    }
}

This is a very simple example obviously, normally you'd send more meta-data to the plugins, or have multiple different interfaces depending on the kinda plugin it is, or have some methods to ask plugins when they're suitable to be used. But this way a user can provide compiled versions of their plugins (in the same language as the core application) - instead of having to provide something like lua scripts

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