Behavior should be specialized depending on the dynamic types of both arguments. Assume I have a Shape class that knows how derive the intersection of any Shapes. Assume I have a Rectangle class, that is extra clever and knows how to intersect Rectangles efficiently.

shapes-class-demo.raku

# Shape ∩ Shape -> Shape
# Shape ∩ Rectangle -> Shape
# Rectangle ∩ Shape -> Shape
# Rectangle ∩ Rectangle -> Rectangle

class Shape {
	#| Universal Shape ∩ Shape --> Shape
	multi method intersect(Shape $s --> Shape){
		return Shape.new
	}
}

class Rectangle is Shape {
	#| Specialized Rectangle ∩ Rectangle --> Rectangle
	multi method intersect(Rectangle $s --> Rectangle){
		return Rectangle.new
	}
}

class Client {
	has @.pairs-of-shapes;
	method intersect-all {
		gather {
			for @!pairs-of-shapes -> ($s1, $s2) {
				take $s1.intersect($s2)
			}
		}
	}
}

use Test;

my @arr of Shape = Shape.new, Rectangle.new;
my @pos = (@arr X @arr);
is-deeply Client.new(pairs-of-shapes => @pos).intersect-all,
		  (Shape.new, Shape.new, Shape.new, Rectangle.new);