HaloO,
John M. Dlugosz wrote:
If the programmer really wants to decrement "10" to "09" she has to
cast that to Str: ("10" as Str)--. So we have "10".HOW === Str
but "10".WHAT === Num Str.
It's behaving as Num ∪ Str, while the declaration Num Str in
juxtaposition means Num ∩ Str.
Hmm? I meant Num ∩ Str. This intersection type is a subtype of
Str and Num without type coercion and it beats both in specificity
when it comes to dispatch.
"10".HOW returns something that does the Metaobject role, which itself
can stringify to the name of the Perl 6 class in this case, but the
details depend of the object system. In a JavaScript or Self object
model, there might not be classes. But what it stringifies to isn't
really discussed.
Yes. It returns the instance manager since instance management is the
prime task of a class.
"10".WHAT returns the undefined prototype of Str. It also stringifies to
the short name of the class.
I had hoped that WHAT denotes a more specific type than HOW. E.g.
subset ThreeChars of Str where {$_.elems == 3}
my ThreeChars $x = 'xxx';
$x.WHAT; # ThreeChars
$x.HOW; # Str
$x === 'xxx'; # false because type i.e. the WHAT
# has to be the same
It were interesting to know what $x.new returns. If that dispatches
to Str the result is '' which is not a ThreeChars. So how does the
subset declaration make it return e.g. ' '? Looks like one needs
more than a subset declaration to make a proper subtype ;)
Using Str by itself is a listop with no parameters and returns the
undefined prototype. So
say "10".WHAT === Str;
prints True. Both refer to the same value: the undefined prototype
object of type Str. If the undefined prototype is guaranteed to be
singular, then =:= would also show True.
Sounds reasonable. The HOW behind Str might e.g. be PerlStr.
say "10".HOW === Str;
prints False. The left side is a Metaobject, the right a Str mixed in
with something that delegates class methods and overrides
stringification etc. The things you can call on them are different. They
could not be implemented as the same object.
How would Str be implemented then? It is more concrete than a role but
more abstract than a class.
Regards, TSa.
--
"The unavoidable price of reliability is simplicity"
-- C.A.R. Hoare
