is_callable()

(PHP 4 >= 4.0.6, PHP 5, PHP 7)

检测参数是否为合法的可调用结构

说明

is_callable(callable $name[,bool $syntax_only= false[,string &$callable_name]]): bool

验证变量的内容能否作为函数调用。这可以检查包含有效函数名的变量，或者一个数组，包含了正确编码的对象以及函数名。

参数

$name

要检查的回调函数。

$syntax_only

如果设置为TRUE，这个函数仅仅验证$name可能是函数或方法。它仅仅拒绝非字符，或者未包含能用于回调函数的有效结构。有效的应该包含两个元素，第一个是一个对象或者字符，第二个元素是个字符。

$callable_name

接受“可调用的名称”。下面的例子是“someClass::someMethod”。注意，尽管 someClass::SomeMethod()的含义是可调用的静态方法，但例子的情况并不是这样的。

返回值

如果$name可调用则返回TRUE，否则返回FALSE。

范例

Example #1is_callable()例子

<?php
//  How to check a variable to see if it can be called
//  as a function.
//
//  Simple variable containing a function
//
function someFunction() 
{
}
$functionVariable = 'someFunction';
var_dump(is_callable($functionVariable, false, $callable_name));  // bool(true)
echo $callable_name, "\n";  // someFunction
//
//  Array containing a method
//
class someClass {
  function someMethod() 
  {
  }
}
$anObject = new someClass();
$methodVariable = array($anObject, 'someMethod');
var_dump(is_callable($methodVariable, true, $callable_name));  //  bool(true)
echo $callable_name, "\n";  //  someClass::someMethod
?>

参见

• function_exists() 如果给定的函数已经被定义就返回 TRUE
• method_exists() 检查类的方法是否存在

If the target class has __call() magic function implemented, then is_callable will ALWAYS return TRUE for whatever method you call it.
is_callable does not evaluate your internal logic inside __call() implementation (and this is for good).
Therefore every method name is callable for such classes.
Hence it is WRONG to say (as someone said):
...is_callable will correctly determine the existence of methods made with __call...
Example:
<?php
class TestCallable
{
  public function testing()
  {
     return "I am called.";
  }
  public function __call($name, $args)
  {
    if($name == 'testingOther') 
    {
        return call_user_func_array(array($this, 'testing'), $args);
    }
  }
}
$t = new TestCallable();
echo $t->testing();   // Output: I am called.
echo $t->testingOther(); // Output: I am called.
echo $t->working();   // Output: (null)
echo is_callable(array($t, 'testing'));    // Output: TRUE
echo is_callable(array($t, 'testingOther')); // Output: TRUE
echo is_callable(array($t, 'working'));    // Output: TRUE, expected: FALSE
?>

is_callable() will try __autoload(), if have one.

is_callable doesn't seem able to resolve namespaces. If you're passing a string, then the string has to include the function's full namespace. 
<?php
namespace foo\bar\baz;
function something ()
{
  return (42);
}
var_dump (is_callable ('something')); // false
var_dump (is_callable ('foo\bar\baz\something')); // true
?>
It's easy to forget, but if you just prepend __NAMESPACE__ to your function name strings you should be fine in most cases.

To corey at eyewantmedia dot com:
your misunderstanding lies in passing in the naked $object parameter. It is correct for is_callable to return FALSE since you cannot 'call an object', you can only call one of its methods, but you don't specify which one. Hence:
is_callable(array($object, 'some_function'), [true or false], $callable_name)
will yield the correct result.
Notice, though, that a quick test I made (PHP 5.0.4) showed that is_callable incorrectly returns TRUE also if you specify the name of a protected/private method from outside of the context of the defining class, so, as wasti dot redl at gmx dot net pointed out, reflection is the way to go if you want to take visibility into account (which you should for true OOP, IMHO).

For closures, the function will return true and $callable_name will be set to "Closure::__invoke".

It seems the only issue left with is_callable() is the disable_functions ini-setting. Apart from that, is_callable() will reliably evaluate whether the passed function or method can be called from within the same context is_callable() was called from, taking visibility and inheritance into account. This includes functions, regular and static methods, magic functions and methods and implemented interfaces (which are regular methods within the implementing class anyway).
<?php
function regular_function() {}
abstract class ParentTest
{
  public function public_parent_method() {}
  protected function protected_parent_method() {}
  public static function static_method() {}
  protected static function protected_static_method() {}
}
class CallableTest extends ParentTest implements Countable
{
  public function __invoke() { } // Introduced in 5.3, see http://php.net/manual/language.oop5.magic.php
  protected function protected_method() { }
  public function is_callable($args)
  {
    return is_callable($args);
  }
  // Countable
  public function count()
  {
    return 1;
  }
}
$o = new CallableTest();
// Regular function:
var_dump(is_callable('regular_function')); // true
// Magic __invoke method:
var_dump(is_callable($o)); // true if PHP >= 5.3, false otherwise
// Countable implementation (regular method really):
var_dump(is_callable(array($o, 'count'))); // true
// Protected method from outside the object's scope:
var_dump(is_callable(array($o, 'protected_method'))); // false
// Protected method from inside the object's scope via public proxy method:
var_dump($o->is_callable(array($o, 'protected_method'))); // true
// Parent's public method
var_dump(is_callable(array($o, 'public_parent_method'))); // true
// Parent's protected method
var_dump(is_callable(array($o, 'protected_parent_method'))); // false
// Parent's protected method via proxy
var_dump($o->is_callable(array($o, 'protected_parent_method'))); // true
// Parent's static public method
var_dump(is_callable('CallableTest::static_method')); // true
// Parent's static protected method
var_dump(is_callable('CallableTest::protected_static_method')); // false
// Parent's static protected method via proxy
var_dump($o->is_callable('CallableTest::protected_static_method')); // true
?>
Tested PHP versions were 5.2.9 on openSUSE 10.3 (x64) and 5.3.1 on Windows Server 2003 (x86).

Be careful when using this function and __call (PHP5). This function will always report true when using __call.
Need a specific function for the purpose of checking if a class method exists explicitly even when using __call.
Haven't ruled out the possibility of the existence of such a function yet. So if someone knows of one, please point it out.

bob at theshirdshift:
"function_exists" doesn't do this, no, but "method_exists" works fine, and is still faster than is_callable:
<?php
function doTimes($start, $end)
 {
  $start_time = explode (" ", $start);
  $start_time = $start_time[1] + $start_time[0];
  $end_time = explode (" ", $end);
  $end_time = $end_time[1] + $end_time[0];
  $time = $end_time - $start_time;
  return $time;
 }
class test
 {
   function test()
   {
     return true;
   }
 }
 
$test = new test;
$callableIsTrue = false;
$startIsCallable = microtime();
for($i = 0; $i < 10000; $i++)
 {
   if(is_callable(array('test', 'test'))) { $callableIsTrue = true; }
 }
$endIsCallable = microtime();
$existsIsTrue = false;
$startExists = microtime();
for($i = 0; $i < 10000; $i++)
 {
   if(method_exists('test', 'test')) { $existsIsTrue = true; }
 }
$endExists = microtime();
$timeIsCallable = doTimes($startIsCallable, $endIsCallable);
$timeExists  = doTimes($startExists, $endExists);
echo "<b>is_callable = ".($callableIsTrue ? "TRUE" : "FALSE")."</b>, \n";
echo "<b>method_exists = ".($existsIsTrue ? "TRUE" : "FALSE")."</b><br>\n";
echo "<br>Did 10000 is_callables in ".$timeIsCallable." seconds";
echo "<br>Did 10000 method_exists in ".$timeExists." seconds";
?>
is_callable = TRUE, method_exists = TRUE
Did 10000 is_callables in 0.410346984863 seconds
Did 10000 method_exists in 0.175447940826 seconds

As empyone noted, early versions of php 5 incorrectly returned true if is_callable checked on a protected or private method. Later versions of php 5 will now only return true if the method is public and can be called externally. I do not know precisely when this behavior was changed, so you may have to test on your own. But sometime between 5.0.4, which empyone said he was using, and 5.2.4 where I tested it myself, the behavior was modified.

Note that is_callable is aware of context, and you can ask it things like parent::__construct from within a child constructor
<?php
  class TestClass extends TestClassParent {
  
    /** @brief Object initialisation callback
      @returns void */
    public function __construct() {
      # do initialisation 
      # ...
      # if we have a parent 
      
      if(is_callable('parent::__construct')) {
      
        # then bubble up 
        
        parent::__construct();
      }
    }
  }
?>

The PHP's function is_callable not verify the visibility of the tested method.
The following function uses the Reflection classes of the PHP5 to check it.
<?php
/**
 * Function is_callback().
 *
 * @param mixed $var Var
 * @return bool
 */
function is_callback($var)
{
  if (is_array($var) && count($var) == 2) {
    $var = array_values($var);
    if ((!is_string($var[0]) && !is_object($var[0])) || (is_string($var[0]) && !class_exists($var[0]))) {
      return false;
    }
    $isObj = is_object($var[0]);
    $class = new ReflectionClass($isObj ? get_class($var[0]) : $var[0]);
    if ($class->isAbstract()) {
      return false;
    }
    try {
      $method = $class->getMethod($var[1]);
      if (!$method->isPublic() || $method->isAbstract()) {
        return false;
      }
      if (!$isObj && !$method->isStatic()) {
        return false;
      }
    } catch (ReflectionException $e) {
      return false;
    }
    return true;
  } elseif (is_string($var) && function_exists($var)) {
    return true;
  }
  return false;
}
?>

is_callable generates an [E_STRICT] error if the tested method cannot be called staticly. (and returns the good value)
I used @is_called 
i'm using php 5.2.1

I have come across a strange oddity in versions around the 4.3.11 mark - I may have missunderstood the purpose of this function but hope this'll be helpful for some.
The point the code below is supposed to illustrate is that in some cases with 
  <? $myFunc = Array( $myObj, 'myMethod' ); ?>
  <? is_callable( $myFunc, true, $callMe ); ?>
will return true, and give you $callMe set to myObj::myMethod but calling 
  <? $callMe(); ?>
doesn't work... however calling
  <? $myFunc[0]->$myFunc[1](); ?>
seems to work fine..
... the reason all the code is down there is I think this oddity is due to how/the order in which I've instantiated my classes or something... 
anyhow... HTH someone! :-)
Code follows:
FILE 1 :
<?
  include('myTools');
  
  $foo = new myClass();
  
  print $foo->getMySource();
  
  class myClass{
    
    var $flibble = 'wibble';
    
    function myClass(
      // Initialise loads of stuff.. including..
      $this->tools = new myTools();
    )
    
    function getMySource(){
      // This just returns the source.. ok, like some HTML to go into an email for example.
      // Some arguments;
      $args  = $this->flibble;
      // Call our Tool that returns the source.. 
      $source = $this->tools->returnSource( Array ( $this, 'someHTML' ), $args );
      // and return it..
      return ( $source );
    }
    
    function someHTML($args){
      // Leave PHP
      ?>
      Here is some HTML.. that we want to build outside a PHP block,
      possibly just cos it's tidier in <B>your favourite text editor</B>.. 
      .. or you want this function to be elsewhere.. for your designers
      to play with etc.. ... incidentally I'd like to say "<?=$args?>" etc.
      <?
      // .. and we're back.
    }
  }
  
?>
FILE 2:
<? 
  /* OK - this is some other big library and a whole load more
    faff but this is the particular function in question... it
    just calls the function it's been asked to and uses an output
    buffer to grab the output and return it as a string rather than
    letting it go to terminal/browser.... useful for grabbing PHP pages
    for spidering, emailing etc. etc. etc..
  */
  
  class myTools(){
    
    function returnSource($func, $args){
      
      if ( is_callable ( $func, true, $callMe ){
        // Start a buffer
        ob_start();
        // Calling the function like this DOESN'T seem to work:
        // ~~~~~~~~
        // "Command not found : myClass::someHTML"
        // $callMe($args);
        // ~~~~~~~~
        // But - what I've discovered is that this behaves fine..
        if ( is_array($func) ){
          $func[0]->$func[1]($args);
        } else {
          $func($args);
        }
        // Then we just carry on with our code.. 
        $rtn =   ob_get_contents();
        ob_clean();
        return ( $rtn );
      } else {
        error_log("Doh!");
      }
    }
  }
  
?>

Revised function with static support:
<?php
  /**
  * The is_callable php function only considers methods declared in the class itself, and ignores the parent's.
  * This version considers all of the hierarchy.
  * 
  * @param (string|Object) $class_name
  * @param string $method_name
  * @param bool $static the method being tested is static.
  */
  public static function isCallable( $class_name, $method_name, $static = false ){
    
    if( !is_string( $class_name ) ){
      $class_name = get_class( $class_name );
    }
    
    // Define Callable
    if( $static ){
      $callable = "{$class_name}::{$method_name}";
    }else{
      $callable = array( $class_name, $method_name );
    }
    
    
    // Check class itself
      if( @is_callable( $callable ) === true ){
        if( $method_name == 'setEmailAddressTypeHash' ) {
          ErrorHandler::preDump($callable);
        }
        return true;
      }
    
    // Check all parents
      while( $parent_class = get_parent_class( $class_name ) ){
        if( @is_callable( $callable ) === true ){
          return true;
        }
        $class_name = $parent_class;
      }
      
    return false;
  }
?>

It's not immediately evident from the content of the article, but implementing __invoke() makes an object callable.
<?php
class ObjectWithInvoke {
 public function __invoke() {}
}
$o = new ObjectWithInvoke();
if (is_callable($o)) echo "true"; else echo "false";
// echoes "true"
?>

The story about __call() is a bit more complicated unfortunately. It will always return true ONLY if you pass an instance of a class, not if you pass the class name itself:
<?php
class MyClass {
  public function method() { }
  public function __call($name, $arguments) { }
}
is_callable([MyClass::class, 'method']); // true
is_callable([new MyClass(), 'method']); // true
is_callable([MyClass::class, 'other']); // false!!!
is_callable([new MyClass(), 'other'])); // true

Please note that the example at comment #104633 is no longer valid with PHP 7 as it seems to be fixed:
PHP 7.0.16-1~dotdeb+8.1
correctly outputs:
bool(true)

Some additional notes about the implementation (PHP 5.6):
- <?php is_callable(array("myclass", "f1")) ?> will return true even if myclass::f1() is not a static method. As such, even if is_callable() will return true, the method cannot be called.
- <?php is_callable(array($object, "f2")) ?> will return true even if $object->f2() cannot be called because of method visibility (e.g. f2() is private or protected).

Example how is_callable works:
<?php
$counter = 0;
class TestClassOne {
  function testMethod(){
    global $counter;
    return ++$counter;
  }
  static function testMethodStatic(){
    global $counter;
    return ++$counter;
  }
}
class TestClassTwo {
  function __invoke() {
    global $counter;
    return ++$counter;
  }
}
function test_function() {
  global $counter;
  return ++$counter;
}
$p1 = 'test_function';
$p2 = new TestClassOne();
$p3 = ['TestClassOne', 'testMethodStatic'];
$p4 = [new TestClassOne(), 'testMethod'];
$p5 = new TestClassTwo();
$p6 = function() {
  global $counter;
  return ++$counter;
};
foreach ([$p1, $p2, $p3, $p4, $p5, $p6] as $p) {
  if(is_callable($p)){
    echo 'is invokable: yes '.$p().PHP_EOL;
  } else {
    echo 'is invokable: no'.PHP_EOL;
  }
}
?>
And output is:
is invokable: yes 1
is invokable: no
is invokable: yes 2
is invokable: yes 3
is invokable: yes 4
is invokable: yes 5

Note that, for the purpose of this function, an abstract method, although necessarily non-callable since it does not have a body, is still considered to be callable:
<?php
abstract class Foo { 
 abstract function bar(); 
}
echo is_callable(array('Foo', 'bar'));
// display: 1
?>

is_callable() does _not_ check wheter this function is disabled by php.ini's disable_functions
use:
<?PHP
function is_disabled($function) {
 $disabled_functions=explode(',',ini_get('disable_functions'));
 return in_array($function, $disabled_functions);
}
?>
I`m running PHP 5.2.4

True that method_exists() is faster than is_callable(). However, is_callable() will be able to correctly recognize method calls handled by __call() in PHP 5, while method_exists() will not.

The way to discover whether a method exists in face of a __call is reflection.
It should be mentioned that although array('Test', 'func') is callable according to this function (where func is a public static method of Test), actually calling this construct as $fn() fails.

I've been spending a month on and off trying to figure out why
is_callable($object, [true or false], $varContainingFunctionName)
returned false when it should not have (ie: $object->FunctionName() was callable), I realized I must have misunderstood its purpose. If you find yourself in the same situation, try
function_exists(string functionname)
or
method_exists ( object object, string method_name )
before you rip your hair out :)

I, too, was wondering whether is_callable or function exists is faster when checking class methods. So, I setup the following test:
<?php
function doTimes($start, $end)
 {
  $start_time = explode (" ", $start);
  $start_time = $start_time[1] + $start_time[0];
  $end_time = explode (" ", $end);
  $end_time = $end_time[1] + $end_time[0];
  $time = $end_time - $start_time;
  return $time;
 }
class test
 {
   function test()
   {
     return true;
   }
 }
 
$callableIsTrue = false;
$startIsCallable = microtime();
for($i = 0; $i < 10000; $i++)
 {
   if(is_callable(array('test', 'test'))) { $callableIsTrue = true; }
 }
$endIsCallable = microtime();
$existsIsTrue = false;
$startExists = microtime();
for($i = 0; $i < 10000; $i++)
 {
   if(function_exists('test::test')) { $existsIsTrue = true; }
 }
$endExists = microtime();
$timeIsCallable = doTimes($startIsCallable, $endIsCallable);
$timeExists   = doTimes($startExists, $endExists);
echo "<b>is_callable = ".($callableIsTrue ? "TRUE" : "FALSE")."</b>, \n";
echo "<b>function_exists = ".($existsIsTrue ? "TRUE" : "FALSE")."</b><br>\n";
echo "<br>Did 10000 is_callables in ".$timeIsCallable." seconds";
echo "<br>Did 10000 function_exists in ".$timeExists." seconds";
?>
This gives the output :
is_callable = TRUE, function_exists = FALSE
Did 10000 is_callables in 0.0640790462494 seconds
Did 10000 function_exists in 0.0304429531097 seconds
So the fact that function_exists is twice as fast is slightly over shadowed by the fact that it doesn't work on class methods, at least not as far as I can tell.

I haven't seen anyone note this before, but is_callable will correctly determine the existence of methods made with __call. The method_exists function will not.
Example:
<?php
class Test {
  public function testing($not = false) {
    $not = $not ? 'true' : 'false';
    echo "testing - not: $not<br/>";
  }
  
  public function __call($name, $args) {
    if(preg_match('/^not([A-Z]\w+)$/', $name, $matches)) {
      $fn_name = strtolower($matches[1]);
      if(method_exists($this, $fn_name)) {
        $args[] = true; // add NOT boolean to args
        return call_user_func_array(array($this, $matches[1]), $args);
      }
    }
    die("No method with name: $name<br/>");
  }
}
$t = new Test();
$t->testing();
$t->notTesting();
echo "exists: ".method_exists($t, 'notTesting').'<br/>';
echo "callable: ".is_callable(array($t, 'notTesting'));
?>
Output:
testing - not: false
testing - not: true
exists:
callable: 1

beware calling is_callable on class that has the same method name will return false, i filed a bug report to be included in function description as example
<?php
class test {
 function test() {
 }
}
$class = new test();
var_dump(is_callable([$class, 'test']));
?>
will return false

I don't know if it is a bug but when you test an array with a class and method, is_callable returns true for non static method.
Consider the following code:
<?php
class A
{
  public static function test()
  {
    echo 'test', '<br>';
  }
  public function hello()
  {
    echo 'hello', '<br>';
  }
}
echo "Static #1: call_user_func(array('A', 'test')) => ", call_user_func(array('A', 'test')), '<br>'; 
echo 'expect is_callable TRUE => ',
  is_callable(array('A', 'test'))
    ? 'TRUE, A::test() is callable statically'
    : 'FALSE, A::test() is not callable statically',
  '<br><br>'
;
echo "Static #2: call_user_func(array('A', 'hello')) => ", call_user_func(array('A', 'hello')), '<br>'; 
echo 'expect is_callable FALSE => ',
  is_callable(array('A', 'hello'))
    ? 'TRUE, A::hello() is callable statically'
    : 'FALSE, A::hello() is not callable statically',
  '<br><br>'
;
$a = new A();
echo "Instance #1: call_user_func(array(\$a, 'test')) => ", call_user_func(array($a, 'test')), '<br>'; 
echo 'expect is_callable TRUE => ',
  is_callable(array($a, 'test'))
    ? 'TRUE, $a::test() is callable'
    : 'FALSE, $a::test() is not callable',
  '<br><br>'
;
echo "Instance #2: call_user_func(array(\$a, 'hello')) => ", call_user_func(array($a, 'hello')), '<br>'; 
echo 'expect is_callable FALSE => ',
  is_callable(array($a, 'hello'))
    ? 'TRUE, $a::hello() is callable'
    : 'FALSE, $a::hello() is not callable',
  '<br><br>'
;
?>
Will output:
Static #1: call_user_func(array('A', 'test')) => test
expect is_callable TRUE => TRUE, A::test() is callable statically
Static #2: call_user_func(array('A', 'hello')) => 
Strict Standards: call_user_func() expects parameter 1 to be a valid callback, non-static method A::hello() should not be called statically in test.php on line 24
hello
expect is_callable FALSE => TRUE, A::hello() is callable statically
Instance #1: call_user_func(array($a, 'test')) => test
expect is_callable TRUE => TRUE, $a::test() is callable
Instance #2: call_user_func(array($a, 'hello')) => hello
expect is_callable TRUE => TRUE, $a::hello() is callable
------------------------------------------------------------
Also note that this works the same for inherited methods (I read other posts suggesting otherwise), and that private methods (static, inherited or both) always return false in any case as expected.
Tested with php 5.6.20.