HaloO,
Smylers wrote:
TSa writes:
... one question remains that might actually make Duncan's proposal
pointless.
Didn't Larry actually accept Darren's proposal and add the C<before> and
C<after> operators?
He did. But I don't understand exactly how the coercive semantics
of the numeric and string comparisons are achieved. I assume there
are protos defined with signature :(Any,Any) that coerce the args
to numeric or string and re-dispatch. Right? IIRC, these protos
kick in when dispatch ends in a draw.
Are the comparison operators available for overloading just like any
other operator
Yes. This feature is used often enough in Perl 5 classes, and I'm
almost certain there are no plans to remove it from Perl 6.
That sounds good and places the numeric and string comparison ops
close to generic. I think that there will be a role as follows:
role Order[Str $lt = '<',
Str $gt = '>',
Str $le = '<=',
Str $ge = '>=',
Str $cmp = '<=>'
Str $eq = '==' ] does Compare[$eq] # provides === and eqv
{
enum <Increase(1) Same(0) Decrease(-1)>;
# these two need to be provided
multi infix<before> ( ::?CLASS $one, ::?CLASS $two ) {...}
multi infix<after> ( ::?CLASS $one, ::?CLASS $two ) {...}
# the other ops can be expressed in terms of before and after
multi infix:«$lt» ( ::?CLASS $one, ::?CLASS $two )
{
$one before $two
}
multi infix:«$gt» ( ::?CLASS $one, ::?CLASS $two )
{
$one after $two
}
multi infix:«$le» ( ::?CLASS $one, ::?CLASS $two )
{
$one !after $two
}
multi infix:«$ge» ( ::?CLASS $one, ::?CLASS $two )
{
$one !before $two
}
multi infix:«$cmp»( ::?CLASS $one, ::?CLASS $two )
{
if $one before $two { return Increase }
elsif $one === $two { return Same }
elsif $one after $two { return Decrease }
else { return undef } # ?
}
}
With that you can write
class Str does Order[|<lt gt le ge leg eq>] {...}
But that is a bit clumsy and I would like to call the role
as does Order[Str] to get the string comparison ops and as
Order[Num] for the numeric ones. Order[Str|Num] would bring
in both and all other Order[Foo] would just get the generic
before and after. How does one write such a role? I mean you
need to match a type parameter with Str and Num and prepare
the corresponding multis for composition.
Regards, TSa.
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