What does the & before the function name signify?
Does that mean that the $result is returned by reference rather than by value? If yes then is it correct? As I remember you cannot return a reference to a local variable as it vanishes once the function exits.
function &query($sql) { // ... $result = mysql_query($sql); return $result; } Also where does such a syntax get used in practice ?
Does that mean that the
$resultis returned by reference rather than by value?
Yes.
Also where does such a syntax get used in practice ?
This is more prevalent in PHP 4 scripts where objects were passed around by value by default.
$a = new stdClass; $a->prop='foo'; function test($b){ $b->prop = 'bar'; } test($a); echo $a->prop; As you can see, the object is passed by-ref :)
To answer the second part of your question, here a place there I had to use it: Magic getters!
class FooBar { private $properties = array(); public function &__get($name) { return $this->properties[$name]; } public function __set($name, $value) { $this->properties[$name] = $value; } } If I hadn't used & there, this wouldn't be possible:
$foobar = new FooBar; $foobar->subArray = array(); $foobar->subArray['FooBar'] = 'Hallo World!'; Instead PHP would thrown an error saying something like 'cannot indirectly modify overloaded property'.
Okay, this is probably only a hack to get round some maldesign in PHP, but it's still useful.
But honestly, I can't think right now of another example. But I bet there are some rare use cases...
Does that mean that the
$resultis returned by reference rather than by value?
No. The difference is that it can be returned by reference. For instance:
<?php function &a(&$c) { return $c; } $c = 1; $d = a($c); $d++; echo $c; //echoes 1, not 2! To return by reference you'd have to do:
<?php function &a(&$c) { return $c; } $c = 1; $d = &a($c); $d++; echo $c; //echoes 2 Also where does such a syntax get used in practice ?
In practice, you use whenever you want the caller of your function to manipulate data that is owned by the callee without telling him. This is rarely used because it's a violation of encapsulation – you could set the returned reference to any value you want; the callee won't be able to validate it.
nikic gives a great example of when this is used in practice.
<?php // You may have wondered how a PHP function defined as below behaves: function &config_byref() { static $var = "hello"; return $var; } // the value we get is "hello" $byref_initial = config_byref(); // let's change the value $byref_initial = "world"; // Let's get the value again and see echo "Byref, new value: " . config_byref() . "\n"; // We still get "hello" // However, let’s make a small change: // We’ve added an ampersand to the function call as well. In this case, the function returns "world", which is the new value. // the value we get is "hello" $byref_initial = &config_byref(); // let's change the value $byref_initial = "world"; // Let's get the value again and see echo "Byref, new value: " . config_byref() . "\n"; // We now get "world" // If you define the function without the ampersand, like follows: // function config_byref() // { // static $var = "hello"; // return $var; // } // Then both the test cases that we had previously would return "hello", regardless of whether you put ampersand in the function call or not. 