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To: "PHP internals" <internals@lists.php.net>, "Stas Malyshev"
 <smalyshev@sugarcrm.com>
References: <CAHpw9Ac0oapNSV=y4Gj3WCdZ1ckik+WOJt-yMdMjGt3u7iJpJg@mail.gmail.com> <545B3900.6070208@sugarcrm.com>
Date: Thu, 06 Nov 2014 13:14:20 +0400
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Message-ID: <op.xowbx6zvc9evq2@nikita-pc>
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Subject: Re: [PHP-DEV] Allow arbitrary expressions when using instanceof
 operator
From: inefedor@gmail.com ("Nikita Nefedov")

On Thu, 06 Nov 2014 13:01:52 +0400, Stas Malyshev <smalyshev@sugarcrm.com>  
wrote:

> Hi!
>
>> What I want to implement is the ability to allow arbitrary expressions  
>> on
>> the second operand, so instead of having to write something like this:
>
> I'm afraid there's a problem with this. Arbitrary expressions include
> constants, right? So what this means:
>
> var_dump($foo instanceof Bar);
>
> is it checking $foo for being instance of class Bar (that's what is
> happening now) or is it taking the value of the constant Bar (whatever
> it is) - since constant is an expression - and using it as a class name
> and then checking if $foo is an instance of that class?
>
> You could of course require the expression to always be enclosed in (),
> but that produces weird syntax where some forms of instanceof work
> without () and some only with (). Given that you can easily assign your
> value to a variable, is it worth it?
>
> Also, you can always use is_a($foo, $bar->getClassName()).


Hey Stas,

You're right about parenthesis - they are required to use expressions.  
Basically when you're in parenthesis - it will only mean that it's an  
expression, otherwise it's a direct class reference. It could be worked  
around by creating a new class of expression (on parser level, say  
expr_not_single_const or anyting like that) that would match any  
expression except constant references, but that's too much I guess.

Also one thing not mentioned in the initial letter - this will also allow  
you to use expressions for new operator in the same way: `new  
(str_replace('/', '\\', $classPath))()` - just an example.

I would say that it's just not logical to have some operator that can  
accept dynamic (runtime-defined) value but not an expression.