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)
