Aaron pointed out:
> But, in terms of constants, it seems to me that there's no
> difference. They both have only one value that is assigned
> when the module/class is parsed.
Well, in *practice* there's no difference, but in their mystical essences,
they're completely different. ;-)
> > I'd do that like so (using Larry's preferred syntax):
> [...]
> > method INIT ($idval) { $.id := $idval }
>
> Hm... that looks to me like a regular ":="; is it?
Yep.
> If so, what good is "is const" if you can override it with
> a ":="? Am I missing something?
That's a binding, not an assignment.
C<is const> means: "Once declared cannot be *assigned* to".
But that doesn't mean one can't *bind* a new value to the variable
(which would retain its C<const>-induced unassignability after the binding).
Consider the following Perl 5:
# CREATE CONSTANT
*constant = \7;
print "$constant\n";
# TRY TO ASSIGN (THROWS EXCEPTION)
eval { $constant = -7 } or print $@;
print "$constant\n";
# TRY TO REBIND (WORKS FINE)
eval { *constant = \-7) } or print $@;
print "$constant\n";
The analogy in Perl 6 would be:
# CREATE CONSTANT
my $constant is const = 7;
print "$constant\n";
# TRY TO ASSIGN (THROWS EXCEPTION)
try { $constant = -7 } catch { print $! }
print "$constant\n";
# TRY TO REBIND (WORKS FINE)
try { $constant := -7) } catch { print $! }
print "$constant\n";
Damian
