Doc #61422 [Opn->Ver]: Clarify when autoloading is triggered

Edit report at https://bugs.php.net/bug.php?id=61422&edit=1

 ID:                 61422
 Updated by:         [email protected]
 Reported by:        danko at very dot lv
-Summary:            Lack of autoload on type hinting breaks class_alias
+Summary:            Clarify when autoloading is triggered
-Status:             Open
+Status:             Verified
 Type:               Documentation Problem
-Package:            SPL related
+Package:            *General Issues
 Operating System:   Linux
 PHP Version:        5.4.0
 Block user comment: N
 Private report:     N

 New Comment:

This has nothing to do with class_exist(), but is rather because
type declarations of free standing functions never trigger
autoloading[1].

[1] <https://3v4l.org/NuX6K>


Previous Comments:
------------------------------------------------------------------------
[2012-05-01 13:51:10] danko at very dot lv

It hit me that:

- The behaviour is consistent with instanceof

- Calling autoload in instanceof is unacceptable (for obvious reasons), no bug here.

- The case with instanceof is much worse, since instead of raising an error instanceof returns a WRONG RESULT and it is the CORRECT BEHAVIOUR.

- This is hardly obvious and is bound to lead to some beautiful glitches.

I therefore propose that a warning is placed on the page for __autoload / spl_autoload_register and/or class_alias (if it is, indeed, the only thing this problem would break).

------------------------------------------------------------------------
[2012-03-16 21:10:16] danko at very dot lv

Sorry, what I meant in the last example is
	// Create a Demo object using "Y",
	// and pass that to function expecting "X"

------------------------------------------------------------------------
[2012-03-16 21:06:27] danko at very dot lv

Description:
------------
I found #39003 which implies that autoload *was* called for type hinting previously and called for removal of this "unnecessary" feature.

I beg to differ. Our framework depends on using class_alias to provide a dynamic modular structure, and one real class may have multiple aliases depending on situation, and these aliases are currently added when needed. Therefore, if an object is creating using alias X (or no alias at all) and is passed to a function expecting the same class under alias Y (and no object was created using that alias) a completely invalid fatal error is raised (see a simplified demo below).

I would also like to point out, that if after calling autoload it turns out that it was not, in fact, an alias, the call will fatally fail anyway, so a really useless autoload will be only called once. I don't see any "resource consumption" problem here.

Test script:
---------------
<?

	class Demo { }
	
	// An "autoload" handler creating an alias for the same class
	spl_autoload_register(function ($class) {
		class_alias('Demo', $class);
	});
	
	// Create a Demo object using "A"
	// and pass that to function expecting "A"
	function success(A $test) {
		echo "Success ".get_class($test)."\n";
	}
	success(new A());
	
	// Create a Demo object using "B",
	// then create another Demo object using "C"
	// and pass that to function expecting "B"
	function also(B $test) {
		echo "Success ".get_class($test)."\n";
	}
	new B();
	also(new C());
	
	// Create a Demo object using "X",
	// and pass that to function expecting "B"
	function fail(X $test) {
		echo "Success ".get_class($test)."\n";
	}
	
	fail(new Y());
	
	// Note that all of these names refer to the same class,
	// and all objects are of the same class



Expected result:
----------------
Success Demo
Success Demo
Success Demo

Actual result:
--------------
Success Demo
Success Demo
PHP Catchable fatal error:  Argument 1 passed to fail() must be an instance of X, instance of Demo given


------------------------------------------------------------------------



--
Edit this bug report at https://bugs.php.net/bug.php?id=61422&edit=1