Match types about fathom

[brendanzab]

Another option might be to use some sort of cond construct that would take boolean predicates. This would allow use to avoid having to implement pattern matching:

const TRIANGLE : u32 = 0u32;
const RECTANGLE : u32 = 1u32;
const CIRCLE : u32 = 2u32;

Point = {
    x: f32be,
    y: f32be,
};

Data = struct {
    shape_type : u32,
    length: u32be,
    data : [cond {
        shape_type == TRIANGLE => [Point; 3],
        shape_type == RECTANGLE => [Point; 4],
        shape_type == CIRCLE => struct { center: Point, radius: f32be },
        else => error,
    }; length],
};

[mikeday]

Looks like a better place to start, and it's still possible to check for exclusive/exhaustiveness.

[brendanzab]

One tricky thing is figuring out to implement this under the hood. At the moment I'm using a reader as an argument to my parser for flexibility purposes, but I can't keep a hold of the current buffer position using that, unlike if I was using a slice or a Cursor.

[brendanzab]

I could do some crazy internal caching, but not sure how that would turn out 🤔

[brendanzab]

Oh wait, for cond this shouldn't actually matter!

[brendanzab]

We might also want to support giving names to the variants:

cond {
    triangle  : shape_type == TRIANGLE  => Triangle,
    rectangle : shape_type == RECTANGLE => Rectangle,
    circle    : shape_type == CIRCLE    => Circle,
}

This would then allow use to generate an enum:

enum DataDataElem {
    Triangle(Triangle),
    Rectangle(Rectangle),
    Circle(Circle),
}