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Subject: Re: [PHP-DEV] Declare minimum PHP version required?
From: larry@garfieldtech.com (Larry Garfield)

On 02/03/2014 09:51 PM, Yasuo Ohgaki wrote:
>
>> I have to agree with Stas and Sara on this one.  This is not the job of
>> the language syntax.  This is the package manager's job; once the code is
>> installed (not compiled, installed), you shouldn't be changing your version
>> anyway without knowing what you're doing / verifying on a test system
>> anyway.
>>
>> If this were more like Javascript's "use strict", where it affected the
>> parsing rules of that file, that would at least be useful (if potentially
>> mind-bendingly painful for the engine; no I'm not suggesting we do that).
>>   But a shortcut for if (version_compare()) die; is not needed, and that
>> would be a dumb way to go about implementing version requirements in the
>> first place.
>
> This assumption is not valid as I already wrote.
> There will be SCL in RHEL7 and there are tools like phpenv.
> Installing PHP does not have to be executing PHP.

I don't know what SCL is, nor what phpenv is.  Thus "installing PHP does 
not have to be executing PHP" makes little sense to me as a sentence.

> Version and module requirement checks are popular and I
> don't think it is dumb at all. It is dumb that if script didn't
> work as it should be due to version mismatch, isn't it?

Well usually it will fatal anyway if it's written for a too-new 
version.  I know software has version checks in it; Drupal (the project 
I work on primarily) has had a version check in it for years... but in 
the installer, not in arbitrary non-installer files.

> BTW, it is not a short cut of version check, but "elimination of
> run time check overheads". Many people don't understand
> what declare() is, it seems.
>
> declare() is compiler directive, *NOT* a function. Thus it could
> instruct what compiler should do at compile time. Since declare()
> is compiler directive, compiler may omit byte code for declare
> block. Therefore, run time overheads of declare block may be
> eliminated with byte code cache.

I can think of exactly one use case for compiling or not compiling a 
given file depending on the version, and that's for function backports 
(like the old PHP_Compat library, or the backport of the password hash 
functions from PHP 5.5.)  Those are trivial enough to just wrap the 
require statement in a version_compare().  Or, really, the opcode 
overhead of that compared to the size of a typical code base these days 
is probably negligible.

> Isn't checking requirements over and over a waste of resources?

Yes. So don't do it. :-)  Really, I have no clue what the use case is here.

--Larry Garfield