Question

Is it possible to use the shorthand ternary to check whether a variable is set or not instead of whether is evaluates to zero or non-zero?

For example, I tried:

$var = 0;
echo (string) $var ?: (string) false ?: 2;

But since both the first two expressions evaluate to "0" or "false", 2 is displayed.

I thought that perhaps casting them to a string would produce different results, but it did not. Zero is zero I suppose.

I’m wanting to use this style when assigning variables such as

$get->var = $get->var ?: $setindb ?: $default;

I want to assign $get->var to $get->var if it is set, otherwise, check if the db has a value, otherwise, use a default.

Edit

I thought I would mention that I know I could do something like

$get->var = (!empty($get->var)) ? $get->var : ( (!empty($setindb)) ? $setindb : $default )

But you be the judge at which is simpler 🙂

Answer 1

The string “0” and “false” are considered FALSE-y (list of false values) values in PHP.

isset() returns TRUE for variables that are set and not NULL. empty() will check that the variable is set and that is isn’t a FALSE value. So it would return TRUE for “0”.

I think that what you want is your third code snippet, but with isset(), rather than empty().

The easiest way to do (with the least amount of brackets) that would be:

$get->var = isset($get->var) ? $get->var : (isset($setindb) ? $setindb : $default);

Since the shorthand tenary returns the first parameter, you can’t use it, because that would be a boolean. ( isset($get->var) ?: $default would return TRUE, FALSE or $default, but never $get->var‘s value. )

---

Edit: Perhaps you’d like something like a coalesce function? PHP doesn’t offer it natively, as far as I know, but it’s trivial to create. Note that this might be a bit ugly, due to its use of passing references to a function. I’d be interested in comments on this (is it as bad as I think it is?).

function coalesce(array $values)
{
    foreach($values as &$value)
    {
        if(isset($value))
            return $value;
    }
    return null;
}
$this->var = coalesce(array(&$this->var, &$setindb, $default));

I haven’t tested the above. Pass variables in the array as references (& symbol). I’m pretty sure it’ll choke on something like coalesce(array(1,"a_string",false));.