On Tue, Jul 19, 2005 at 07:25:35PM +0100, Matthew Hodgson wrote:
: Hi all,
:
: I've spent some of the afternoon wading through A12 and S10 trying to
: thoroughly understand scope in perl 6, in light of the death of use vars
: and the addition of class (as well as package & module) namespaces.
:
: In the process I came up against some confusion concerning how the default
: package namespace should work. Currently, pugs does:
:
: % pugs -e '$main::foo="foo"; say $foo'
: foo
:
: which contradicts S10, which states:
:
: The "::*" namespace is not "main". The default namespace for the main
: program is "::*Main".
:
: This turned out to be an oversight - but there was then confusion as to
: how one actually refers to variables in the "::*Main" namespace, as if
: $Foo::bar looks up the ::Foo object and fetches $bar from it, then
: presumably $*Main::foo should look up the ::*Main object, and fetch $foo
: from it.
:
: However (from #perl6):
:
: <autrijus> Arathorn: when you see $Foo::bar, it means looking up the ::Foo
: object, then fetch $bar from it
: <autrijus> and ::Foo, just like %Foo, can be lexical or package scoped or
: global (%*Foo)
: <autrijus> to restrict the lookup to ::*Foo you can't use the ordinary
: qualifying syntax, I think.
: <autrijus> but I may be completely wrong
: <Arathorn> so it sounds as if to get the variable $bar from the global
: packagename ::*Foo (or just *Foo if disambiguation is not necessary),
: you'd use $*Foo::bar then.
: <autrijus> that may be the case, yes.
: <autrijus> $?Foo::bar means $?bar in Foo::
: <autrijus> but $*Foo::bar can't mean $*bar in Foo::
: <autrijus> because Foo:: will never contain a $*bar.
: <autrijus> so it must mean $bar in *Foo::
: <autrijus> this is very weird.
:
: So the question is: what is the correct syntax for referring to package
: variables in the default namespace?
The * looks like a twigil but it isn't really. It's short for "*::",
where the * is a wildcard package name, so in theory we could have
$=*foo, meaning the $=foo in the *:: package. (But most of the
twigils imply a scope that is immiscible with package scope.)
: Also, what is the correct syntax for referring to package variables in
: your 'current' namespace? $::foo? $?PACKAGENAME::foo?
: $::($?PACKAGENAME)::foo? %PACKAGENAME::<foo>?
That's currently:
$OUR::foo
though presumably
$::($?PACKAGENAME)::foo
would also work as a symbolic reference. I'm not sure whether $::foo
is usefully distinct from $foo these days. It almost seems to imply
that ::foo is in type space and we have to dereference it somehow.
There's a sense in which :: only implies type space after a name.
We somehow seem to have the situation where :: is simultaneously
trying to be a leading sigil, a trailing sigil, and a separator.
Larry
