Hi Ilja,
Ilija Tovilo wrote:
Hi internals
I'd like to announce the match expression RFC that replaces the switch
expression RFC I announced a few weeks ago.
New: https://wiki.php.net/rfc/match_expression
I like this proposal in general, I've wanted something like Haskell and
Rust's case/match statements for years but never got round to proposing
them. I do have some comments and concerns however:
* While I like the Rust-like feature of being able to use it both as a
statement and as an expression, I share others' concern that it is
inconsistent with PHP's existing statements. I would suggest either
an RFC to apply this to other statements, or to take it out for now.
* It is a shame you don't suggest taking this opportunity to add pattern
matching. We already have destructuring assignment syntax in PHP,
albeit only for arrays, so why not support pattern-matching for arrays
in `match` right now? I guess variable scope might be awkward (matched
values would leak into function scope), but it is for other statements
already. If we do not add pattern matching right now, perhaps we can
design the syntax so it doesn't prevent adding it later? Using a
keyword prefix (e.g. `let`) in future means we end up with two kinds
of arm (one with === behaviour, one with pattern-matching behaviour),
but wouldn't it be simpler to have just one?
* Relatedly, it is a shame not to have guards. `switch (true)` is not a
very nice idiom, `match (true)` is worse (no handling of truthiness),
and neither provides the full power that patterns + guards together
provide, where you can neatly combine pure value matching with
arbitrary boolean checks. Sure, you can write `($foo === BAR) =>`,
but you might as well use an if-statement then. I shouldn't let
perfect be the enemy of the good, but I think there's so much more
that could be done here. Note that even the limited possible patterns
without inventing new syntax (a plain variable, and an array pattern)
are more useful if guards are available.
* It is unfortunate if we have to add another reserved word… I don't
know if there'd be a way to do this with `switch` that isn't
confusable with the existing statement, though.
Thanks,
Andrea
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