// Regression test for issue #18320.
struct CustomStruct {
pub:
	a int
	b string
}

interface BaseInterface {
	a int
}

fn callback[T](ctx BaseInterface, cb fn (T)) {
	$if T is BaseInterface {
		cb(ctx)
	}
}

fn main() {
	custom := CustomStruct{
		a: 5
		b: 'test'
	}
	callback(custom, fn (ctx CustomStruct) {
		println(ctx)
	})
}