Scala does it by pulling out the keyword arguments to variables so that your example would become { val x$1 = B() val x$2 = A() A(.one = x$2, .two = x$1)

Scala does it by pulling out the keyword arguments to variables so that your example would become { val x$1 = B() val x$2 = A() A(.one = x$2, .two = x$1) } This maintains left-to-right evaluation order while allowing you to pass arguments in any order. There is probably some dark and forbidden reason why C++ can't do that. ETA: That's basically what the post does.