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Re: Virtual methods

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Luke Palmer
May 18, 2005 07:51
Re: Virtual methods
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On 5/18/05, Aaron Sherman <> wrote:
> In Perl 6, I don't think we need to tag methods as "virtual" like C++
> does, since we have the handy yadda, yadda to do that for us.
> However, there is a variant of C++'s virtual that I'd love to see. By
> default a role cannot override the methods of a class, but if it could
> override those methods specifically marked with the virtual trait, then
> we could define stub methods in classes that don't have a specific
> behavior until a more concrete role is mixed in.
> This gives you a form of auto-loading like delegation, but with less
> storage overhead (since there's no encapsulation until you need it).
> Here's an example:
>         role X {
>                 has Str $.string handles<ucfirst>;
>                 # I'll write something like an accessor to avoid brining
>                 # up some questions around how virtual methods interact
>                 # with auto-accessors just yet.
>                 method setstring(Str $string) { $.string = $string }
>         }
>         class Y {
>                 method setstring(Y $me: Str $string)
>                     is virtual {
>                         $me does X;

Except that mixins like this always treat things as "virtual". 
Whenever you mixin a role at runtime, Perl creates an empty, anonymous
subclass of the current class and mixes the role in that class.  Since
roles beat superclasses, you'll always override your own methods.


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