[PHP] Invalid argument supplied for foreach()

Question

It often happens to me to handle data that can be either an array or a null variable and to feed some foreach with these data.

$values = get_values();

foreach ($values as $value){
  ...
}

When you feed a foreach with data that are not an array, you get a warning:

Warning: Invalid argument supplied for foreach() in [...]

Assuming it's not possible to refactor the get_values() function to always return an array (backward compatibility, not available source code, whatever other reason), I'm wondering which is the cleanest and most efficient way to avoid these warnings:

• Casting $values to array
• Initializing $values to array
• Wrapping the foreach with an if
• Other (please suggest)

Answer 1

Personally I find this to be the most cleanest - not sure if it's the most efficient, mind!

if (is_array($values))
{
    foreach ($values as $value)
    {
        ...
    }
}

The reasons for my preference is so you're not allocating an empty array when you've got nothing to begin with anyway.

Answer 2

First of all, every variable must be initialized. Always.
Casting is not an option.
if get_values(); can return different type variable, this value must be checked, of course.