Sure. Then, if you're set on using lambdas, I'd recommend this, to at least take away the ability to choose <T> from the caller. static Shape<?> Circle(int

Sure. Then, if you're set on using lambdas, I'd recommend this, to at least take away the ability to choose <T> from the caller. static Shape<?> Circle(int x, int y, int r) { return (circle, rectangle) -> circle.apply(x, y, r); } static Shape<?> Rectangle(int x, int y, int w, int h) { return (circle, rectangle) -> rectangle.apply(x, y, w, h); }