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up vote 1 down vote favorite

How do I pass a variable to create_function() ?

I have something like this:

function my_hook_function(){
  $var = 10;
  apply_filters('hook', $var);
  return $var;
}


$variable = 5;
$function = create_function('', 'return $variable;');

add_filter('hook', $function); 

echo my_hook_function();

but it doesn't work :( theoretically the output should be 5

add_filter() is a wordpress function that allows you to change stuff around :)

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4 Answers

up vote 2 down vote accepted

There are two problems here. The first one is that you need to tell php what parameters get passed to the 'created' function, or reference them as a global inside of the body. The second is that you are expecting $var to be modified by the created function, but you are not passing it a reference. the created function simply returns the new variable and you do nothing with it. 

function my_hook_function(){
  $var = 10;
  $var = apply_filters('hook', $var);
  return $var;
}

/* This will return 5 by dividing the passed value by 2 and returning the result */
$function = create_function('$variable', 'return $variable/2;');    
add_filter('hook', $function);
echo my_hook_function();

/* This will return 5 by referencing the global $variable */
$variable = 5;
$function = create_function('', 'global $variable; return $variable;');
add_filter('hook', $function);
echo my_hook_function();

Note that if you run this code exactly like this that both of the filters will be added to the 'hook' hook.

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up vote 4 down vote 
$outsideVarName = 3434;
$function = create_function('$insideFunctionVarName', 'return $insideFunctionVarName;');
echo $function($outsideVarName);
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up vote 3 down vote

Reading the manual for create_function the usage for passing $variable to the function would be as follows:

$variable = 3434;
$function = create_function('$v', 'return $v;');

echo $function($variable);

EDIT

Changed $variable inside the create_function call to make it a bit clearer of proper usage and avoid confusion.

UPDATE

Given the comment below, here is an updated version:

$variable = 3434;
$function = create_function('$v', 'return $v;');

function myTest($function, $var) {
    echo $function($var);
}

myTest($function, $variable); // should echo 3434

Not sure if that is what you want, I will refrain from guessing further till you show the actual context you are working in.

Update 2

Doing some research, is there a reason you do not just use it in this manner:

add_filter('something', create_function('$v', 'return $v;'));

From what I could find that should work...

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hm.. the problem is that i can call $function like that :( the created function is passed as a argument to another function, and needs to be a string... –  Alex Sep 2 '10 at 22:26
 
Show your full code please or at least the context you are working in (IE the function you are passing $function to). I cannot accurately diagnose an issue if you only give me 1/4 of the problem. –  Brad F Jacobs Sep 2 '10 at 22:28
 
ok, edited. it's wordpress-related, but I don't think wp has anything to do with the errors i get –  Alex Sep 2 '10 at 22:35
 
Well it depends on how add_hook uses the variable $function. Chances are it thinks that $function should be the name of a function and not an actual function. –  Brad F Jacobs Sep 2 '10 at 22:37
 
yes, the 2nd paramater should be the function name, but isn't that that $function is ? –  Alex Sep 2 '10 at 22:39
show 3 more comments
up vote 1 down vote

I think what you really want is

$function = create_function('', "return $variable;");

or 

$function = create_function('', 'return ' . $variable . ';');

i.e. you want to capture the value of the variable into the function when created. Since a number converted to a string is the same as its source representation, simply interpolating it into the source of the function is sufficient. For strings and arrays, some quoting will be necessary.

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