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Postings from August 2012
Ricardo Signes wrote:
> This seems like complete madness.
(I know I am quoting your words out of context, but they sound funnier that way.)
Do we really need smart match at all?
The three advantages to smart match I’ve seen are:
• Junctive operations: ~~ @foo
• Accepting qr// or sub{} from the caller and using it on the rhs
• when(3) which is nice and short.
(I don’t consider ‘we need a generic way of asking whether two objects match’ to be valid, because ‘match’ on its own is meaningless.)
The first one we’ve solved with Perl6::Junction.
The second one I don’t feel comfortable with at all. It is a very specific use case. Wrapping qr//s in sub{} I would consider the correct approach. The problem with any interface that accepts qr//-or-sub{} is that classes implementing one type of overloading can’t add the other without potentially breaking things. So it makes module authors’ lives harder. I’m simply not convinced that this feature is a pressing need. We already have generic matchers. They are called subs.
The third one actually has nothing to do with smart match at all. It’s a ‘when’ problem. If we really really don’t want to have to write when($_==3), then we could copy the precedent set by flipflop and split.
if (1..2) means if ($.==1 .. $.==2)
split ' ' is special
$x = ' '; split $x does something different
and implement two syntactic special cases:
# literal numbers
when(0)
when(1)
when(0xff)
when(0b101110)
when(023476)
# literal strings
when('foo')
when("foo")
when(q "foo")
when(qq "foo")
and *nothing* else. Everything else would be a boolean, including when($foo). Anything else is madness; it really is.
Then we can just deprecate ~~.
Those who say they want
when(num(3))
can write
sub num { $_ == $_[0] }
instead of
sub num { my $arg = shift; sub { $_[0] == $arg } }
which I think is an improvement.
But that doesn’t work with lexical $_, so let’s deprecate that, too.
(And make when do a simple next, and make given respond to next.)
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