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Date: Thu, 08 Apr 2010 15:08:36 -0700
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Subject: Autoboxing with type hints
From: jeremy@pinacol.com (Jeremy)

I'm not sure if this is a bug, an oversight, or something that is known 
and deemed not-worth-fixing, so I thought I would ask here first.

Consider the SPL_Types extension.  This extension introduces some 
classes that override assignment in order to do some type-checked 
autoboxing:

$int = new SplInt;
$int = 5;		
//$int is not overwritten with scalar '5', but is now SplInt(5).

$int = 'foo';
//throws UnexpectedValueException: Value not an integer

That is a pretty neat thing.  However, I would see the primary use-case 
for this as the following:

function foo(SplInt $int)
{
	//some code
}

foo(5);	


Unfortunately, this produces "Catchable fatal error: argument 1 passed 
to foo() must be an instance of SplInt, integer given".  This, however, 
works:

$int = new SplInt;
$int = 5;
foo($int);

Does it seem like a good idea for the type checking mechanism for type 
hinted parameters to check whether the hinted class has overridden 
assignment, and if so, delegate the type checking to that mechanism? 
For example,

foo('bar');

would yield 'UnexpectedValueException: Value not an integer', rather 
than the catchable fatal error associated with the type hinted parameter.

Or, perhaps there is something that the extension itself could be doing 
to make this happen?  Or, perhaps this intentionally does not happen?

I know that genuine scalar type hints are kinda-sorta-maybe on the table 
for a future version, but as of right now using the SPL Types to emulate 
that in a performant way would be pretty neat.


Thanks,
Jeremy

P.S. - As a side note - I wonder whether it would be possible to make 
accessible from userspace the functionality that SPL_Types uses to 
override assignment?  For example, you could have an __assign($value) 
magic method that, if present, would be invoked when attempting to 
assign a value to an existing object:

class Foo
{
	public function __assign($value)
	{
		echo $value;
	}
}

$foo = new Foo;
$foo = 'foobar';	//outputs foobar
echo ($foo instanceof Foo);	//output 1

That's not something I'm really requesting - just an interesting 
thought.  I'm sure that operator overloading has been brought up and 
shot down before, and that functionality is dangerously close to such. 
But yeah.