Namely,
1. When you pass the object variable, the formal parameter behaves like a C++ pointer to the object inside the function.
2. When you pass the object variable by reference, the formal parameter behaves like a C++ reference to a pointer to the object inside the function.
The syntax is different between the languages, but the semantics are identical.
I have $scriptVar and $_SESSION['sessionVar'] and I want to bind them together using a custom SessionManager class. I want to selectively prefer the content of either var upon the situation - to be able to "link" either $scriptVar to $_SESSION['sessionVar'] (thus override the "content" of $scriptVar with the content of $_SESSION['sessionVar']) or to link $_SESSION['sessionVar'] to $scriptVar (vice versa).
But as somebody mentioned here already, PHP's references aren't really references, so the simplistic way to do this is impossible to use. I came up with the following:
<code>
... class def and other method declarations ...
public static function &linkVar($varName, &$var = null, $overrideSessionValue = false) {
if ($overrideSessionValue === true) {
$_SESSION[$varName] =& $var;
} else {
return $_SESSION[$varName];
}
}
... class def and other method declarations continue ...
</code>
Now, when I want to override the Session value, I simply call the function with three params, first being the session var name, second being a reference to the $scriptVar and the third a "true" telling the function to link $_SESSION[$varName] to $var, which links to $scriptVar and therefore to link $_SESSION[$varName] to $scriptVar. When I want to link it the other way, to override $scriptVar's value with $_SESSION[$varName] and link them together, I call the function with only the $varName argument and assign it's output to $scriptVar as a reference. Tested, working... at least under PHP 5.3.
What References are not: References.
References are opaque things that are like pointers, except A) smarter and B) referring to HLL objects, rather than memory addresses. PHP doesn't have references. PHP has a syntax for creating *aliases* which are multiple names for the same object. PHP has a few pieces of syntax for calling and returning "by reference", which really just means inhibiting copying. At no point in this "references" section of the manual are there any references.
The example given in the text:
<?php
function foo(&$var)
{
$var =& $GLOBALS["baz"];
}
foo($bar);
?>
illustrates (to my mind anyway) why the = and & should be written together as a new kind of replacement operator and not apart as in C, like $var = &$GLOBALS["baz"];
Using totally new terminology:
To me the result of this function is not surprising because the =& means 'change the "destination" of $var from wherever it was to the same as the destination of $GLOBALS["baz"]. Well it 'was' the actual parameter $bar, but now it will be the global at "baz".
If you simply remove the & in the the replacement, it will place the value of $GLOBALS["baz'] into the destination of $var, which is $bar (unless $bar was already a reference, then the value goes into that destination.)
To summarize, =, replaces the 'destination's value; =&, changes the destination.
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