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Postings from October 2015
* Dave Mitchell <davem@iabyn.com> [2015-10-07 10:30]:
> I think 95% of what people actually *want* a smartmatch system for
> is so that they can write code of one of these three forms:
Mostly agree.
> Why get rid of the smartmatch operator? I've never really seen the
> point of it, apart from being something that exposes the underlying
> mechanism of when(), c.f. readline() for <>. If we do keep it, then it
> should have exactly the same semantics as I've described above for
> when().
Disagree. Plenty of times I’ve written interfaces that let the user say
watch to match, so I’ve written various ad-hoc incarnations of “if you
pass a string, it will be compared exactly, if you pass a regexp object
it will be matched, if you pass a sub it will be called and the return
value will be checked for truthiness”. It would be real nice if all of
that could be replaced with just “pass a smarmatch operand” and all the
code implementing this sort of thing could go away.
(I reserve comment on any specifics of your proposal; I only wanted to
address your premises.)
* Eirik Berg Hanssen <Eirik-Berg.Hanssen@allverden.no> [2015-10-07 20:25]:
> If you are doing away with polymorphism, why squeeze these three
> different semantics into a single keyword? […]
>
> ncase (0) {...}
> scase ("foo") {...}
> when (undef) {...}
> when (/foo/) {...}
At that point would go for making `when` exactly like `if`, except with
an implicit trailing `break`, yielding
when ($_ == 0) {...}
when ($_ eq "foo") {...}
when (not defined) {...}
when (/foo/) {...}
The `ncase` keyword is nothing more than an unfamiliar spelling of `==`
on top of this `when`, since it’s all purely syntactically determined
anyway. And the familiar spelling of `==` is perfectly serviceable as
far as I’m concerned. Under this proposal I wouldn’t even special-case
smartmatch – it would require explicitly saying
when ($_ ~~ $something) {...}
Many things in Perl already know to check $_ in absence of an explicitly
named variable, so the main difference between implicitly smartmatching
`when` and the just-an-`if`-with-implicit-break `when` is
when (0) {...}
when (1) {...}
when ("foo") {...}
when ("bar") {...}
vs
when ($_ == 0) {...}
when ($_ == 1) {...}
when ($_ eq "foo") {...}
when ($_ eq "bar") {...}
Whereas, in contrast, stuff like this is a wash:
when (undef) {...}
when (/foo/) {...}
vs
when (not defined) {...}
when (/foo/) {...}
Regards,
--
Aristotle Pagaltzis // <http://plasmasturm.org/>
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