How to make sort_custom function in GDNative?

[gscoders2]

I see that in include/core/Array.hpp there is void sort_custom(Object *obj, const String &func);but not sure how to use it, any body can help me?

[Zylann]

In GDScript, sort_custom expects an object, and a method of that object to be called for comparing elements of the array to sort.

So as it stands in the script API, that function requires you to do the following:

• Implement a sorting method to one of your custom classes with the following signature: bool compare(Variant a, Variant b), which should return true if a < b. Variant is used because Array does not enforce the type of items in it.
• Register that function so Godot can call it
• Have an instance of the custom class (if you sort within a method of such a class you already have an instance)
• Use the function on the array like so: array.sort_custom(obj, "compare"). If you do it from within the same class that contains the compare method, obj can be this.

Summary:

class YourClass : public SomeBaseClassThatIsOrInheritsObject {
    GODOT_CLASS(YourClass, SomeBaseClassThatIsOrInheritsObject )
public:
    void _init() {
        //...
    }

    bool compare(Variant a, Variant b) {
        // Let's say for example a and b are vectors (casting is automatic, but we assume it wont fail)
        Vector2 va = a;
        Vector2 vb = b;
        // And you could want to compare their X coordinate
        return a.x < b.x;
    }

    void whatever(Array array) {
        array.sort_custom(this, "compare");
    }

    static void _register_methods() {
        godot::register_method("compare", &YourClass::compare);
    }
};

(I did not test that code, only wrote it from memory of what I think it could be)

If however you can afford not having to use Array, you can use C++ usual sorting methods with an std::vector<T> with the std::sort function. Godot's bound types are nice to communicate with the engine but they aren't efficient to do complex operations on in C++. It might even be a bit faster to do that on large arrays if you first convert the Array, but it depends what you want this for.

[gscoders2]

@Zylann thanks for answer, I have already tried this but without success, lib is compiling without errors but when I using function (in your case it would be "whatever") in Godot from lib that contain sort_custom inside, game run is crashing

[Zylann]

You would be hitting another problem then, I strongly suggest you use a debugger to see where it's crashing, otherwise none of the C++ errors will tell you anything (not using a C++ debugger is like trying to test GDScripts by exporting the game and run it to see if it passes or breaks^^"). You could seek help about the crash on Discord GDNative channel

edit: added _init to the example because it's always required otherwise it, well, crashes