A safer way to extract PHP vars

Many people advise against using extract() mainly for 2 reasons:

• Its unsafe when extracting user input such as $_GET and $_POST
• It makes the code hard to maintain because tracking variables that come out of extract() calls are difficult

Despite the controversy I feel it is a very convenient tool especially when needing to extract a lot of variables for use in templates. So heres how I use it, which solves both of the problems above. Let’s say you have two variables “username” and “password” coming in…

extract(afilter($_POST,"username,password"));
echo "Username is $username";

This will only extract the variables you specify, which makes it safe to use. And, it serves as documentation for which variables are being extracted. Anyone searching for a specific variable name, will quickly realize where it’s coming from.

Here’s the code for afilter()

/**
 * Array Filter: filter out keys not specified
 * Usage: extract(afilter($_GET,'var1,var2,...'));
 */
function afilter($data, $allowedKeys)
{
    if(is_string($allowedKeys)) 
        $allowedKeys=explode(",",$allowedKeys);
    return array_intersect_key($data,array_flip($allowedKeys));

}

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