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Subject: Re: [PHP-DEV] Invokation on __toString() for object used as array
 key
From: smalyshev@sugarcrm.com (Stas Malyshev)

Hi!

> I’m not sure that’d make much sense. The object isn’t the key, the
> value the magic method returns is. It would be quite odd to do this:
> 
> $someArray = [$my__hashImplementingObject => 1]; 
> var_dump($someArray);
> 
> And see something like this, because we’ve called a hash function:
> 
> array(1) { ["ec10e5a66e281d105f302cacfb1aaca8"]=> int(0) }

The hash doesn't have to be a nonsensical hex value, it can be something
like "My Object Number 42" if you want to. The difference is that
__toString is for human reading, and it's not always suitable for
hashing purposes. Just read the docs on any of the languages that have
separate hash method - they all have the same argument, there's a
different between printing an object for output and using the object as
a key.

> I don’t really see what advantage this has over the normal
> __toString. Furthermore, having a special method we use to cast here
> that’s used nowhere else seems weird.

That's the point - it's not a cast. It's an operation that requires
object's identity. Again, given that so many languages have it, I don't
think it's really that weird. I think it's pretty natural.

> Now, if we were to add actual object key support, that I might like.
> But if we’re going to keep with just integers and strings, I’d much
> prefer to just support __toString here. I think users are smart
> enough to understand that PHP arrays only have string or int keys, so
> it casts to a string.

The problem is you mix here two completely different domains. On one
hand, you may want the object to have text representation for output
purposes - say, XML object would have XML output as it's string rep. On
other hand, I don't think you want to use 100K XML as a key, because
using as a key is a completely different issue. Converting to string is
a hack that mixes two different problems into one method, and that's why
it will lead to problems. The solution for this problem is known and
widely used - have a separate hash method. With PHP, you can actually
have a luxury of using a human-readable keys while still keeping them
nice and clean and independent from string representation. And if you
want maximum efficiency, you could switch to ints instead.
-- 
Stanislav Malyshev, Software Architect
SugarCRM: http://www.sugarcrm.com/