How can I reference C# objects in GDScript (and vice versa)?

Question

I am using Godot Engine 3.0.6 Mono for Windows x64. I am prototyping the majority of my project in C# before I rewrite the game in C++ for release. I installed this plugin mostly to help with testing and debugging value-sensitive functionality. To make this possible however, I will need to be able to make references to my C# classes from GDScript (or vice versa) for binding commands. I could not find any instructions on how to do this in the official documentation. Can this be done currently in either direction?

Note: If the references are made from C# to GDScript classes, I need to be able to cast the Nodes respectively to make function calls.

Answer 1

I figured out how this works both ways after a couple of days.

It is not immediately obvious and the GDScript interpreter will yell at you, but as long as your C# objects are included in the .csproj file and the class itself extends Object, you can call any method in the C# script.

The C# API adds a nice way of calling GDScript instance functions, which is are the Godot.Object methods Call(), CallDeferred(), and Callv().

E.G. given:

SampleGD.gd

func from_csharp(content):
    print(content)

Then in C# you would obtain a reference to this object in the scene or use ResourceLoader to load a new instance. After such, you could do:

SampleCS.cs

var sampleGD = FindNode("SampleGD");
sampleGD.Call("from_csharp", "Hello from C#!");