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Subject: Re: [PHP-DEV] [RFC] Using objects as keys
From: smalyshev@sugarcrm.com (Stas Malyshev)

Hi!

> Put another way, I think a key question here is:
> 
> class Foo {
>    public $bar;
> }
> 
> $a = new Foo;
> $a->bar = 'baz';
> $b = new Foo;
> $b->bar = 'baz';
> 
> $arr[$a] = true;
> $arr[$b] = true;
> 
> 
> Does $arr now contain one value or two?

That depends on the semantics of class Foo. If Foo is something like
UString, then it should contain one value, since UString is a value
object (https://en.wikipedia.org/wiki/Value_object) - or at least it
should be. However, if Foo represents something having separate identity
- i.e. it's a Person class and 'bar' represents name - then of course it
should contain two values, since the name is not the sole source of
Person's identity. So the decision is on you as a programmer.

And to give you the tool to make this decision and let PHP engine know
about is exactly the point of this RFC.

> If the desire is for it to contain 2, then spl_object_hash($a) already 
> has that covered, I think.
> 
> If the desire is for it to contain 1, then the proposal sounds like a 
> way to normalize Foo::stringifiedValueObjectEquivalent().

You can describe it as such, but in a proper standartized way and with
syntax that allows you to use same syntax constructs on all keys and not
have to check each time if it's a special value and call a special
function on it (same purpose as for __toString).
-- 
Stanislav Malyshev, Software Architect
SugarCRM: http://www.sugarcrm.com/