Hi, not sure if this question belongs here, I beli...

# getting-started

[Wyatt Kennedy]

Hi, not sure if this question belongs here, I believe it to be a general kotlin issue I'm not understanding. I'm using a custom scripting host, but I don't think it's relevant here. If you think it is, let me now and I'll move the question to that channel. The script host uses this as the root object class :

open class Pipeline : DeclareContext() {
    val vertexShader = VertexShader()
    val fragmentShader = FragmentShader()

    fun vertexShader(init : VertexShader.() -> Unit) {
        vertexShader.apply(init)
    }

    fun fragmentShader(init : FragmentShader.() -> Unit) {
        fragmentShader.apply(init)
    }
}

and I have this in the script file:

val color by declaring(Vec4)
vertexShader {
    val inPosition by input(Vec2)

    // val testUbo by uniform(Vec4)

    position <= vec4(inPosition, 0.0f, 1.0f)
}

The IDE helps me out and confirms that inside the block, this is VertexShader , i.e not nullable. That call to input() is an error when run and the IDE agrees with a red squiggle, because apparently I don't have a matching provideDelegate function. The implementation that should apply looks like this:

inline operator fun <reified T, U> InputStruct<T>.provideDelegate(thisRef : VertexShader, prop : KProperty<*>) : T where T : StructImpl<T>, T : Expression<U>{
    val struct = this.def.create(prop.name, null)
    if (ref != null) {
        ref.inputs += struct
    } else {
        throw RuntimeException("This block shouldn't bee nullable?")
    }
    return struct
}

It is roughly equivalent to the provideDelegate for the return value of the declaring in the outer scope, but that one does not complain. The error complains that the thisRef of my provideDelegate is not nullable. When I make thisRef VertexShader?, it compiles without issue but the thisRef passed in is null and I need the VertexShader in this case. Am I not understanding something about the semantics around provideDelegate or function receivers?

[Wyatt Kennedy]

The specific error in case that provides any clues:

Property delegate must have a 'provideDelegate(Nothing?, KProperty<*>)' method. None of the following functions is suitable: 
public inline operator fun <reified T : StructImpl<Vec2>, U> Shader.InputStruct<Vec2>.provideDelegate(ref: VertexShader, prop: KProperty<*>): Vec2 where T : Expression<IVec2> defined in org.ksentiment.shaderdsl

[Wyatt Kennedy]

In true rubber duck fashion, I figured it out after I pulled together my question. The clue was the Nothing? expected in the signature. thisRef is only provided when you declare a delegated property on a class. thisRef is Nothing? if the delegate is declared anywhere else (function, lambda, etc), even if there is a this in the context. The ONLY exception appears to be in a script host, where the root object is treated as a class declaration as well. I was able to work around this by updating the input() method on my Shader such that I put this on the object returned, like so:

class InputStruct<T : Struct<T>>(val shader : Shader, val def : StructDef<T>)
fun <T : Struct<T>> input(def : StructDef<T>) = InputStruct(this, def)

And then updating the provideDelegate method so that thisRef : Any? since I was not going to use it.

[Youssef Shoaib [MOD]]

You could've also used context receivers for this on the provideDelegate method FYI