WordPress has this great filtering system which allows you to write plugins. Yesterday, I was writing a plugin that has the ability for other plugins to change it's behaviour.
For the particular functionality, it would be very nice to use two parameters, which should both be changable.
Standard PHP
In standard PHP, you could do:
function doit($in, &$var2){
$var2=true;
return $in+1;
}
$changed=false;
echo doit(1,$changed);
echo $changed; |
function doit($in, &$var2){
$var2=true;
return $in+1;
} $changed=false;
echo doit(1,$changed);
echo $changed;
Pass by reference: Not working with WordPress
The WordPress apply_filter and add_filter functions do not allow variable passing by reference. Therefore, the following code will not work.
function doit($in, &$var2){
$var2=true;
return $in+1;
}
add_filter('myfilter','doit',10,2);
$changed=false;
echo apply_filters('myfilter',1,$changed);
echo $changed; |
function doit($in, &$var2){
$var2=true;
return $in+1;
} add_filter('myfilter','doit',10,2);
$changed=false;
echo apply_filters('myfilter',1,$changed);
echo $changed;
Dirty solution
You could use $GLOBALS to overcome this problem. I would not recommend this method, as it's not flexible, not safe to re-use and requires the function and the main code to be synchronized.
function doit($in){
global $changed;
$changed=true;
return $in+1;
}
add_filter('myfilter','doit');
$changed=false;
echo apply_filters('myfilter',1);
echo $changed; |
function doit($in){
global $changed;
$changed=true;
return $in+1;
} add_filter('myfilter','doit');
$changed=false;
echo apply_filters('myfilter',1);
echo $changed;
The good solution
The correct solution to this problem, is to combine all variabled in one array, and use this array as the first variable.
Example 1: For a few parameters
function doit($in){
list($in,$var2)=$in;
$var2=true;
return array($in,$var);
}
add_filter('myfilter','doit');
$changed=false;
list($in,$changed)=apply_filters('myfilter',array(1,$changed));
echo $in;
echo $changed; |
function doit($in){
list($in,$var2)=$in;
$var2=true;
return array($in,$var);
} add_filter('myfilter','doit');
$changed=false;
list($in,$changed)=apply_filters('myfilter',array(1,$changed));
echo $in;
echo $changed;
Example 2: For more complex situations
function doit($in){
$in['changed']=true;
$in['in']+=1;
return $in;
}
add_filter('myfilter','doit');
$changed=false;
$in=1;
extract( apply_filters('myfilter',compact('in','changed')) );
echo $in;
echo $changed; |
function doit($in){
$in['changed']=true;
$in['in']+=1;
return $in;
} add_filter('myfilter','doit');
$changed=false;
$in=1;
extract( apply_filters('myfilter',compact('in','changed')) );
echo $in;
echo $changed;
This last method may impose a security risk if you use third party plugins.
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