Seriously, tho, I'm not sure I understand the constantness part.
sub foo($x = 1) {...} # A6 syntax
sub foo(?$x = 1) {...}
I read the above as saying $x is indeed constant, but if it's not explicitly placed by the caller, we're going to pretend the caller passed us a 1.
No. I read that as: $x is a constant variable. If the caller passes an argument (by position or name) then that argument is bound to $x. If they don't pass a suitable argument, then $x is *not* bound, but simply initialized to 1.
Likewise, I read
sub foo($x //= 1) {...}
as saying the value stored in $x is a constant, but if the caller passed an undefined value (or didn't pass anything at all), we're going to instead pretend they passed us a (still-constant) 1. I'm not sure why that violates any rules.(?)
//= means "assign to lvalue unless lvalue is defined". So I read that as:
$x is a constant variable. Bind the corresponding argument to $x and then assign 1 to it if its value is undef. But the container bound to $x is bound as a constant, so it *can't* be assigned to.
I guess we could say that, in a parameter declaration, //= means "Bind the lvalue (i.e. the parameter). If the bound value is undef, unbind the lvalue, and then initialize it with the rvalue".
But that's horribly complex.
Damian
