is_a和instanceof有什么区别? [英] What is the difference between is_a and instanceof?

问题描述

我知道 instanceof 是一个运算符，并且 is_a 是一种方法.

I am aware that instanceof is an operator and that is_a is a method.

该方法的性能是否降低?您想使用什么?

Is the method slower in performance? What would you prefer to use?

推荐答案

更新

自PHP 5.3 .9 ，is_a()的功能已更改.以下原始答案指出，is_a() 必须接受Object作为第一个参数，但是PHP版本> = 5.3.9现在接受可选的第三个布尔参数$allow_string(默认为)允许比较字符串类名称:

As of PHP 5.3.9, the functionality of is_a() has changed. The original answer below states that is_a() must accept an Object as the first argument, but PHP versions >= 5.3.9 now accept an optional third boolean argument $allow_string (defaults to false) to allow comparisons of string class names instead:

class MyBaseClass {}
class MyExtendingClass extends MyBaseClass {}

// Original behavior, evaluates to false.
is_a(MyExtendingClass::class, MyBaseClass::class);

// New behavior, evaluates to true.
is_a(MyExtendingClass::class, MyBaseClass::class, true);

instanceof和is_a()之间的新行为的主要区别在于，instanceof将始终检查目标是否是指定类(包括扩展类)的实例化对象，而is_a()仅要求$allow_string参数设置为默认值false时，将实例化该对象.

The key difference in the new behavior between instanceof and is_a() is that instanceof will always check that the target is an instantiated object of the specified class (including extending classes), whereas is_a() only requires that the object be instantiated when the $allow_string argument is set to the default value of false.

原始

实际上，is_a是一个函数，而instanceof是一种语言构造. is_a会慢得多(因为它具有执行函数调用的所有开销)，但是在任何一种方法中，总的执行时间都非常短.

Actually, is_a is a function, whereas instanceof is a language construct. is_a will be significantly slower (since it has all the overhead of executing a function call), but the overall execution time is minimal in either method.

从5.3版开始不再使用，因此不必担心.

It's no longer deprecated as of 5.3, so there's no worry there.

但是有一个区别. is_a作为函数将一个对象作为参数1，并将一个字符串(变量，常量或文字)作为参数2.所以:

There is one difference however. is_a being a function takes an object as parameter 1, and a string (variable, constant, or literal) as parameter 2. So:

is_a($object, $string); // <- Only way to call it

instanceof将对象作为参数1，并且可以将类名(变量)，对象实例(变量)或类标识符(类名(不带引号写成))作为参数2.

instanceof takes an object as parameter 1, and can take a class name (variable), object instance (variable), or class identifier (class name written without quotes) as parameter 2.

$object instanceof $string;      // <- string class name
$object instanceof $otherObject; // <- object instance
$object instanceof ClassName;    // <- identifier for the class

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