Anonymous functions
Anonymous functions, also known as closures, allow the creation of functions which have no specified name. They are most useful as the value of callback parameters, but they have many other uses.
Anonymous functions are implemented using the Closure class.
Example #1 Anonymous function example
<?php
echo?preg_replace_callback('~-([a-z])~',?function?($match)?{
????return?strtoupper($match[1]);
},?'hello-world');
//?outputs?helloWorld
?>Closures can also be used as the values of variables; PHP automatically converts such expressions into instances of the Closure internal class. Assigning a closure to a variable uses the same syntax as any other assignment, including the trailing semicolon:
Example #2 Anonymous function variable assignment example
<?php
$greet?=?function($name)
{
????printf("Hello?%s\r\n",?$name);
};
$greet('World');
$greet('PHP');
?>Closures may also inherit variables from the parent scope. Any such variables must be passed to the use language construct. From PHP 7.1, these variables must not include superglobals, $this, or variables with the same name as a parameter.
Example #3 Inheriting variables from the parent scope
<?php
$message?=?'hello';
//?No?"use"
$example?=?function?()?{
????var_dump($message);
};
$example();
//?Inherit?$message
$example?=?function?()?use?($message)?{
????var_dump($message);
};
$example();
//?Inherited?variable's?value?is?from?when?the?function
//?is?defined,?not?when?called
$message?=?'world';
$example();
//?Reset?message
$message?=?'hello';
//?Inherit?by-reference
$example?=?function?()?use?(&$message)?{
????var_dump($message);
};
$example();
//?The?changed?value?in?the?parent?scope
//?is?reflected?inside?the?function?call
$message?=?'world';
$example();
//?Closures?can?also?accept?regular?arguments
$example?=?function?($arg)?use?($message)?{
????var_dump($arg?.?'?'?.?$message);
};
$example("hello");
?>The above example will output something similar to:
Notice: Undefined variable: message in /example.php on line 6
NULL
string(5) "hello"
string(5) "hello"
string(5) "hello"
string(5) "world"
string(11) "hello world"Inheriting variables from the parent scope is not the same as using global variables. Global variables exist in the global scope, which is the same no matter what function is executing. The parent scope of a closure is the function in which the closure was declared (not necessarily the function it was called from). See the following example:
Example #4 Closures and scoping
<?php
//?A?basic?shopping?cart?which?contains?a?list?of?added?products
//?and?the?quantity?of?each?product.?Includes?a?method?which
//?calculates?the?total?price?of?the?items?in?the?cart?using?a
//?closure?as?a?callback.
class?Cart
{
????const?PRICE_BUTTER??=?1.00;
????const?PRICE_MILK????=?3.00;
????const?PRICE_EGGS????=?6.95;
????protected?$products?=?array();
????
????public?function?add($product,?$quantity)
????{
????????$this->products[$product]?=?$quantity;
????}
????
????public?function?getQuantity($product)
????{
????????return?isset($this->products[$product])???$this->products[$product]?:
???????????????FALSE;
????}
????
????public?function?getTotal($tax)
????{
????????$total?=?0.00;
????????
????????$callback?=
????????????function?($quantity,?$product)?use?($tax,?&$total)
????????????{
????????????????$pricePerItem?=?constant(__CLASS__?.?"::PRICE_"?.
????????????????????strtoupper($product));
????????????????$total?+=?($pricePerItem?*?$quantity)?*?($tax?+?1.0);
????????????};
????????
????????array_walk($this->products,?$callback);
????????return?round($total,?2);
????}
}
$my_cart?=?new?Cart;
//?Add?some?items?to?the?cart
$my_cart->add('butter',?1);
$my_cart->add('milk',?3);
$my_cart->add('eggs',?6);
//?Print?the?total?with?a?5%?sales?tax.
print?$my_cart->getTotal(0.05)?.?"\n";
//?The?result?is?54.29
?>Example #5 Automatic binding of $this
<?php
class?Test
{
????public?function?testing()
????{
????????return?function()?{
????????????var_dump($this);
????????};
????}
}
$object?=?new?Test;
$function?=?$object->testing();
$function();
????
?>The above example will output:
object(Test)#1 (0) {
}Output of the above example in PHP 5.3:
Notice: Undefined variable: this in script.php on line 8
NULLAs of PHP 5.4.0, when declared in the context of a class, the current class is automatically bound to it, making $this available inside of the function's scope. If this automatic binding of the current class is not wanted, then static anonymous functions may be used instead.
Static anonymous functions
As of PHP 5.4, anonymous functions may be declared statically. This prevents them from having the current class automatically bound to them. Objects may also not be bound to them at runtime.
Example #6 Attempting to use $this inside a static anonymous function
<?php
class?Foo
{
????function?__construct()
????{
????????$func?=?static?function()?{
????????????var_dump($this);
????????};
????????$func();
????}
};
new?Foo();
?>The above example will output:
Notice: Undefined variable: this in %s on line %d
NULLExample #7 Attempting to bind an object to a static anonymous function
<?php
$func?=?static?function()?{
????//?function?body
};
$func?=?$func->bindTo(new?StdClass);
$func();
?>The above example will output:
Warning: Cannot bind an instance to a static closure in %s on line %dChangelog
Version | Description |
|---|---|
7.1.0 | Anonymous functions may not close over superglobals, $this, or any variable with the same name as a parameter. |
5.4.0 | Anonymous functions may use $this, as well as be declared statically. |
5.3.0 | Anonymous functions become available. |
Notes
Note: It is possible to use func_num_args(), func_get_arg(), and func_get_args() from within a closure.
← Internal (built-in) functions
? 1997–2017 The PHP Documentation GroupLicensed under the Creative Commons Attribution License v3.0 or later.
本文档系腾讯云开发者社区成员共同维护，如有问题请联系 cloudcommunity@tencent.com
