Re: Adding explicit intent for SWITCH/CASE fall through?

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]