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Postings from March 2005
As an addendum, my idea would also apply to non-attribute variables.
If you say 'my %abc' in a method or sub, and later say 'return %abc',
then a reference to %abc will be returned by default.
So its not like I'm treating attributes differently.
-- Darren Duncan
At 3:27 PM -0800 3/17/05, Darren Duncan wrote:
>It occurs to me that I may have requested something before that
>would cause more problems than it solves if implemented. So I have
>a different idea that would hopefully be efficient, powerful, and
>easy to learn. In short, make it work much like Perl 5.
>
>The idea is Perl methods and subs will always return references or
>scalars by default, just as method/sub arguments always take
>references or scalars by default; so we have symmetry between the
>in/out. And they would do this the same way regardless of the
>caller scalar/list context.
>
>If the writer of a method/sub wants to return a copy of a
>non-trivial structure like a hash or array, they explicitly copy it
>and return the copy. This is elegant because when they are
>explicitly copying, they can also fully control to what depth in a
>tree-like structure the items have either their values or their
>references copied.
>
>For example, with the same $:foo, @:bar, %:baz attributes ...
>
>These would return references to the structure root, in all contexts:
>
> return \$self.:foo;
> return $self.:bar;
> return $self.:baz;
> return \$:foo;
> return @:bar;
> return %:baz;
>
>These would return a new structure with level-1 copies of the
>elements, but if any elements are references then the copies point
>to the same things in all contexts:
>
> return $self.:foo;
> return [$self.:bar];
> return {$self.:baz};
> return $:foo;
> return [@:bar];
> return {%:baz};
>
>The exact syntax could vary. The above would scale to, say,
>explicit 2-dimensional copy similarly to Perl 5, like this:
>
> return [$self.:bar.map:{ [$_] }];
> return [@:bar.map:{ [$_] }];
>
>Now, I am operating under the assumption here that in Perl 6, the
>line between having a reference to something or having that thing is
>blurred, and so there is no need to do explicit dereferencing; eg,
>no @{} or %{}.
>
>All that the caller context would then determine is whether what the
>method/sub returned is flattened or not; the caller context would
>not determine whether the method/sub returns a copy or a reference.
>
>Question: Is there a trait for a sub/method that specifies whether
>it forces a scalar or list context?
>
>Any opinions on this?
>
>-- Darren Duncan
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