如何在PHP中实现回调? [英] How do I implement a callback in PHP?

问题描述

如何用PHP编写回调?

How are callbacks written in PHP?

推荐答案

该手册可互换地使用术语回调"和可调用"，但是，回调"传统上是指类似于函数指针，引用函数或类方法以供将来调用.自PHP 4以来，这已允许使用函数式编程的某些元素.其风味是:

The manual uses the terms "callback" and "callable" interchangeably, however, "callback" traditionally refers to a string or array value that acts like a function pointer, referencing a function or class method for future invocation. This has allowed some elements of functional programming since PHP 4. The flavors are:

$cb1 = 'someGlobalFunction';
$cb2 = ['ClassName', 'someStaticMethod'];
$cb3 = [$object, 'somePublicMethod'];

// this syntax is callable since PHP 5.2.3 but a string containing it
// cannot be called directly
$cb2 = 'ClassName::someStaticMethod';
$cb2(); // fatal error

// legacy syntax for PHP 4
$cb3 = array(&$object, 'somePublicMethod');

这是通常使用可调用值的安全方法:

This is a safe way to use callable values in general:

if (is_callable($cb2)) {
    // Autoloading will be invoked to load the class "ClassName" if it's not
    // yet defined, and PHP will check that the class has a method
    // "someStaticMethod". Note that is_callable() will NOT verify that the
    // method can safely be executed in static context.

    $returnValue = call_user_func($cb2, $arg1, $arg2);
}

现代PHP版本允许上面的前三种格式直接作为$cb()调用. call_user_func和call_user_func_array支持上述所有条件.

Modern PHP versions allow the first three formats above to be invoked directly as $cb(). call_user_func and call_user_func_array support all the above.

请参阅: http://php.net/manual/en/language. types.callable.php

注释/注意事项:

1. 如果函数/类已命名空间，则字符串必须包含标准名称.例如. ['Vendor\Package\Foo', 'method']
2. call_user_func不支持通过引用传递非对象，因此您可以使用call_user_func_array，或者在更高的PHP版本中，将回调保存到var并使用直接语法:$cb();
3. 带有 __invoke()的对象方法(包括匿名函数)属于可调用"类别，可以使用相同的方式使用，但我个人不将其与传统的回调"术语相关联.
4. 旧版create_function()创建一个全局函数并返回其名称.它是eval()的包装，应改用匿名函数.

1. If the function/class is namespaced, the string must contain the fully-qualified name. E.g. ['Vendor\Package\Foo', 'method']
2. call_user_func does not support passing non-objects by reference, so you can either use call_user_func_array or, in later PHP versions, save the callback to a var and use the direct syntax: $cb();
3. Objects with an __invoke() method (including anonymous functions) fall under the category "callable" and can be used the same way, but I personally don't associate these with the legacy "callback" term.
4. The legacy create_function() creates a global function and returns its name. It's a wrapper for eval() and anonymous functions should be used instead.

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