module main

interface Backend {}

struct MetalBackend {}

struct NullBackend {}

fn make_backend() Backend {
    return MetalBackend{}
}

fn main() {
    mut backend := make_backend()
    if mut backend is MetalBackend {
        println('metal')
    } else {
        println('not-metal')
    }
    if mut backend is NullBackend {
        println('null')
    } else {
        println('not-null')
    }
}