Lambda Functions in PHP aren't Logical

Question

Note: I have condensed this article into my person wiki: http://wiki.chacha102.com/Lambda - Enjoy

I am having some troubles with Lambda style functions in PHP.

First, This Works:

$foo = function(){ echo "bar"; };
$foo();

Second, This Works:

class Bar{
    public function foo(){
       echo "Bar";
    }

Third, This works:

$foo = new stdClass;
$foo->bar = function(){ echo "bar"; };
$test = $foo->bar;
$test();

But, this does not work:

$foo = new stdClass;
$foo->bar = function(){ echo "bar"; };
$foo->bar();

And, this does not work

class Bar{
    public function foo(){
       echo "Bar";
    }
$foo = new Bar;
$foo->foo = function(){ echo "foo"; };
$foo->foo(); // echo's bar instead of Foo.

My Question is Why?, and how can I assure that both this:

$foo->bar = function(){ echo "test"; };
$foo->bar();

and this

$foo = new Bar;
$foo->bar();

are called properly? Extra Points if you can point to documentation stating why this problem occurs.

This has more to do with how you cannot override methods of classes dynamically in PHP which is time and time again a source of frustration for me. I end up using arrays (or one of many other "solutions") to dynamically build "things" containing data and functions. Arrays don't work well for auto completion and you lose a lot of other functionality. It's been 10 years since you asked, nothing has changed significantly. If you want to redefine methods after object instantiation you have to use properties instead (ie. you simply can't redefine methods), and properties must be called differently. — Joel M
– Joel M, Commented Feb 6, 2020 at 19:43

cletus · Accepted Answer · 2010-01-17 07:29:24Z

9

This is an interesting question. This works:

$a = new stdClass;
$a->foo = function() { echo "bar"; };
$b = $a->foo;
$b(); // echos bars

but as you say this doesn't:

$a = new stdClass;
$a->foo = function() { echo "bar"; };
$a->foo();

If you want an object to which you can dynamically call members, try:

class A {
  public function __call($func, $args) {
    $f = $this->$func;
    if (is_callable($f)) {
      return call_user_func_array($f, $args);
    }
  }
}

$a = new A;
$a->foo = function() { echo "bar\n"; };
$a->foo2 = function($args) { print_r($args); };
$a->foo();
$a->foo2(array(1 => 2, 3 => 4));

But you can't replace callable methods this way because __call() is only called for methods that either don't exist or aren't accessible (eg they're private).

answered Jan 17, 2010 at 7:29

cletus

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1 Comment

Tyler Carter Over a year ago

This along with other comments let me set up a stdObj class that I can use to reliably create a object without a class (kind of). Thanks!

Ignacio Vazquez-Abrams · Accepted Answer · 2010-01-17 07:08:44Z

3

Functions and methods are treated differently in PHP. You can use runkit_method_add() to add a method to a class, but I know of no way to add a method to an instance.

answered Jan 17, 2010 at 7:08

Ignacio Vazquez-Abrams

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2 Comments

Tyler Carter Over a year ago

It just seems weird. If there isn't a method by the name of bar, it should look for variable bar and see if it is callable, so this line $foo->bar() works.

Ignacio Vazquez-Abrams Over a year ago

You aren't necessarily wrong. But the Zend engine isn't built that way.

Alix Axel · Accepted Answer · 2010-01-17 19:13:04Z

1

Interesting question although I see no reason why this should work:

class Bar{
    public function foo(){
       echo "Bar";
    }
$foo = new Bar;
$foo->foo = function(){ echo "foo"; };
$foo->foo(); // echo's bar instead of Foo.

I had a similar problem with __invoke(), and I've also not been able to solve it:

class base {
    function __construct() {
        $this->sub = new sub();
    }

    function __call($m, $a) {
    }
}

class sub {
    function __invoke($a) {
    }
}

$b = new base();
$b->sub('test'); // should trigger base::__call('sub', 'test') or sub::__invoke('test')?

Solution? Never use __invoke()! :P

edited Jan 17, 2010 at 19:13

answered Jan 17, 2010 at 11:33

Alix Axel

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Comments

NullUserException · Accepted Answer · 2011-11-13 18:18:18Z

1

The closest you could get to make this happen would be by using the __call overload to check if a property contains a closure:

class what {
  function __call($name, $args) {
    $f= $this->$name;
    if ($f instanceof Closure) {
      $f();
    }
  }
}

$foo = new what();
$foo->bar = function(){ echo "bar"; };
$foo->bar();

Though bear in mind the following note from the docs:

Anonymous functions are currently implemented using the Closure class. This is an implementation detail and should not be relied upon.

Reference: Anonymous functions

edited Nov 13, 2011 at 18:18

NullUserException

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answered Jan 17, 2010 at 7:18

leepowers

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3 Comments

Tyler Carter Over a year ago

Another option would to use the is_callable statement. I'm not sure if that will tell me if it is a closure though.

leepowers Over a year ago

This still won't quite work - if there's a method declaration for foo() the __call() won't be called.

Tyler Carter Over a year ago

I'm not too concerned about overriding a method. I'll come back in the morning, this code might work. Would just have to create a class like stdCallableObj that would act as a stdClass when I want to assign closures to it.

Alfred · Accepted Answer · 2012-08-18 09:43:57Z

1

The OP has already presented the solution:

$foo = new stdClass;
$foo->bar = function(){ echo "bar"; };
$test = $foo->bar;
$test();

I.e., any property that contains an anon function has an inherent ambiguity because adding parenthesis after the property name tells PHP that you are calling a method, and not invoking an anon function in a property. To resolve this ambiguity, you must add a degree of separation by storing the property into a local variable first, and then invoking the anon function.

You just have to look at the class property as a property instead of as "a property callable as a method" no matter what it's contents are and assume that php is going to look for a real class method if you put parenthesis after the property.

edited Aug 18, 2012 at 9:43

Alfred

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answered Feb 27, 2011 at 3:11

Wayne Fincher

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Comments

Natalie Adams · Accepted Answer · 2010-06-02 20:14:44Z

0

To me it seems like a bug rather than a "quirk":

<?php
$t = new stdClass;
$t->a = function() { echo "123"; };
var_dump($t);
echo "<br><br>";
$x = (array)$t;
var_dump($x);
echo "<br><br>";
$x["a"]();
echo "<br><br>";
?>

object(stdClass)#1 (1) { ["a"]=> object(Closure)#2 (0) { } } 

array(1) { ["a"]=> object(Closure)#2 (0) { } } 

123

It is there, I just don't think that PHP knows how to run it.

answered Jun 2, 2010 at 20:14

Natalie Adams

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Comments

erisco · Accepted Answer · 2010-06-02 20:31:44Z

0

Consider this:

<?php

class A {

    public $foo

    public function foo() {
        return 'The method foo';
    }

}

$obj = new A;
$obj->foo = function() { return 'The closure foo'; };

var_dump($obj->foo());

Do you mean $obj->foo() the closure or $obj->foo() the method? It is ambiguous and PHP makes the decision that you mean the method. To use the closure, you have to disambiguate what you mean. One way you can do this is by using a temporary variable as you have done. Another way is to use call_user_func($obj->foo).

I do not know of any other easy way.

answered Jun 2, 2010 at 20:31

erisco

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