Lua functions can't be used as Callable

[illarn]

I couldn't figure out how to connect a lua function to a godot signal, e.g.

  node.resized:connect(function() end)

gives invalid argument error in to_variant()

I've seen #196, but solution given there only works for lua functions accessed in godot.
If there is an already working solution I'd propose adding into the readme (since it's a pretty common pattern), if not, having a way to convert lua functions to callable would be much appreciated

[gilzoide]

Hey @illarn , thanks for the report.
Right now, there's no way to create a Callable from a Lua function in Lua code. Best you can do is create a method in a LuaScript and use it instead of the function directly.

We could make this conversion automatic when running code inside Lua, but I don't really like this level of automatic behavior where things change depending on context (in Lua vs in GDScript). Too easy to hit hard to find bugs, as well as making code harder to follow.
One thing I do like and is really easy to do is add a constructor for Callable that accepts a LuaFunction, so we can do like:

node.resized:connect(Callable(function() end))

Any thoughts on how we should address this LuaFunction -> Callable conversion from Lua code?

[illarn]

I agree that implicit conversion would not be practical, adding a callable constructor from a lua function sounds like a great solution, that's the first thing I tried when encountering this. I'll try to add this and make a PR if I'd have time today

[gilzoide]

I'll try to add this and make a PR if I'd have time today

Nice, thanks a lot! I'll give you the hint that VariantType::construct would be the perfect place for that.

By the way, if you bump into the problem of the LuaFunction being destroyed before the Callable is called, we may need to create a CallableCustom that holds either a Ref<LuaFunction> or the sol::protected_function directly to keep the reference alive.

[illarn]

By the way, if you bump into the problem of the LuaFunction being destroyed before the Callable is called, we may need to create a CallableCustom that holds either a Ref<LuaFunction> or the sol::protected_function directly to keep the reference alive.

Hello! I've made #224 with a working solution, although with some nuances (explained in the description and comments)

[gilzoide]

Closing this, since the PR was merged.
Cheers \o/