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Postings from May 2005
David Storrs wrote:
> Let's move this away from simple types like Str and Int for a moment.
If you consider them simple...
> Tell me what this does:
>
>
> class Tree {
> method bark() { die "Cannot instantiate a Tree--it is abstract!" }
> }
> class Birch {
> method bark() { return "White, papery" }
> }
> class Oak {
> method bark() { return "Dark, heavy" }
> }
> class Dog {
> method bark() { print "Woof, woof!"; return "bow wow" }
> }
Four 'pure' classes so far.
> class AlienBeastie isa Tree isa Dog {}
Here you get an error/warning of a composition time conflict between
&Tree::bark and &Dog::bark. BTW, it's 'is' not 'isa'. My preferred
syntax for multiple inheritance is the junctive notation 'is Tree & Dog'
for subclassing because it nicely allows for superclassing with
'is Tree | Dog'.
> class WhiteAlienBeastie isa Birch isa Dog {}
Same for &Birch::bark and &Dog::bark.
> class HeavyAlienBeastie isa Oak isa Dog {}
Same.
> sub Foo(Tree|Dog $x) { $x.bark() }
This might dispatch correctly for 'pure' Trees, Dogs etc.
but not for your mixed classes above.
Regards,
--
TSa (Thomas Sandlaß)
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