Hi Mike,
On 20/10/2019 01:39, Mike Schinkel wrote:
Not yet having experience working on PHP's parser I do not know how it is
configured nor what about the design of PHP requires keywords unable to be used
as constants, class names, function or method names. I know this is a tangent
but that seems like a requirement designed to simplify the parser maybe, and
not because of any logical requirement. So I assume whatever word was used for
this would also have to be a reserved keyword? Or not?
I don't know the full implications in the parser, but at the language
level, any constant can technically appear where this keyword would.
That is, the following is valid right now:
const fallthrough=null;
fallthrough;
It doesn't do anything, but it's valid because any expression on its own
is a valid statement, and a constant on its own is a valid expression.
Interestingly, that actually makes a single keyword *more* appealing to
me, because it means you can get *forwards* compatibility by writing this:
if ( PHP_VERSION < 80000 && ! defined('fallthrough') ) {
define('fallthrough', null);
}
switch ( $x ) {
case 1:
stuff();
fallthrough;
case 2:
moreStuff();
break;
}
For this common case where the new keyword is just a no-op, you then
have code that supports and works identically across a range of versions:
* On versions without the keyword, the constant expression is a no-op
(and may even be optimised out by OpCache?)
* On versions where the keyword is present but optional, the define is
skipped, and the keyword is a no-op
* On versions (or external tooling) where omitting the keyword is a
warning, or even an error, the keyword indicates intent
Regards,
--
Rowan Tommins (né Collins)
[IMSoP]
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