Hi, Nikita
2015-02-20 9:26 GMT-03:00 Nikita Popov <nikita....@gmail.com>:
>
> I think we all agree that it would be nice to not be so strict about
> reserved keywords in some places. As such this RFC hinges on questions of
> implementation.
>
> The RFC uses a purely lexer-based approach, which is nice in principle,
> because ext/tokenizer benefits from it as well.
>
> The disadvantage of doing this in the lexer and in the scope that you're
> proposing (i.e. including class names) is that it requires reimplementing
> quite a number of parser rules via lookahead in the lexer. This means that
> a) the implementation depends on a complete understanding of the PHP
> syntax, otherwise we'll miss edge cases or be too strict in others and
> b) may limit us in future, because we may not be able to introduce syntax
> that can't be reasonably recognized with simple lexer state management or
> lookahead.
>
> To give you an example of a), your patch currently handles a single
> interface name properly
>
> nikic@saturn:~/php-src$ sapi/cli/php -r 'class Foo implements Interface
> {}'
> Fatal error: Interface 'Interface' not found in Command line code on line 1
>
> but fails as soon as you implement multiple interfaces:
>
> nikic@saturn:~/php-src$ sapi/cli/php -r 'class Foo implements Interface,
> Array {}'
> Parse error: syntax error, unexpected 'Array' (T_ARRAY), expecting
> identifier (T_STRING) or namespace (T_NAMESPACE) or \\ (T_NS_SEPARATOR) in
> Command line code on line 1
>
> So, I'm sure this can be worked around with a couple of new lexer rules,
> I'm just trying to show the systematic issues of this approach.
>
Yes, in fact this was an easy fix, thanks for pointing that out. Now, about
the major issue regarding future languages changes:
>
> An example for b) is harder to come by (as I'm not terribly familiar with
> what we can easily detect in the lexer and what we can't). One thing that
> comes to mind is supporting a short lambda syntax like the one available in
> Hack:
>
> (ClassName $a, $b, $c, $d) ==> $a
>
> As this has no prefixing "function" or similar, I suspect that it may be
> rather hard to detect that "ClassName" is actually a class name here and
> requires special treatment. Un-reserving class names now may make features
> like this impossible (or unnecessarily hard) to implement in the future.
>
>
This is a very legit problem, thanks for raising it so early.
> Due to these issues, I don't like the RFC in the current form - I think
> it's too ambitious. Class names simply occur in too many and diverse places.
>
> I would suggest going with a more limited approach instead, which targets
> only method and class constant names. I.e. the label after -> and :: should
> not be reserved (we already do this for ->) and the label after "function"
> and "const" shouldn't be either. Of course this would also allow defining
> global reserved-keyword function/const names as well, so we might want to
> check their names against the list of reserved keywords. Though even that
> is just a courtesy to the user, e.g. it's already possible to define and
> access reserved-keyword constants using define() and constant().
>
> Nikita
>
We still have some time before the feature freeze. I'll give it some more
thought on the argument list detection problem. If nothing good comes, I'll
revert the proposal to it's previous version tailoring only class|object
members declaration and access.
I think we both already agree that the less ambitious proposal wouldn't
offer any drawback and would have many benefits specially now that we are
discussing necessary RFCs that could globally reserve even more words:
- https://wiki.php.net/rfc/reserve_more_types_in_php_7
- https://wiki.php.net/rfc/reserve_even_more_types_in_php_7
- https://wiki.php.net/rfc/in_operator
Cheers,
Márcio
