How to evaluate function only once in ternary operators?

Question

I wonder if I can make a single-line ternary operator that checks the value returned by a function, and uses it?

Let's check this example (PHP) code:

return get_db_row($sql_parameters) ? get_db_row($sql_parameters) : get_empty_row();

my purpose is to return get_db_row() , but if it is empty, then return an empty row.

But, I think, this line will call get_db_row() twice. Is it right ?

I want to call it once. One solution could be storing the return value in a variable like this:

$row = get_db_row($sql_parameters);
return $row ? $row : get_empty_row();

But can I do this in one line?

Something like :

return ($row = get_db_row()) ? $row : get_empty_row();

is it possible ?

Thanks for any help !

Answer 1

You have it correct. The following line will only call the function once:

return ($row = get_db_row()) ? $row : get_empty_row();

Some code to prove this:

$counter = 0;
function test() {
    global $counter;
    $counter++;
    return true;
}

$var = ($ret = test()) ? $ret : 'bar';
echo sprintf("#1 called the function %d times\n", $counter);

$counter = 0;
$var = ($ret = test()) ? test() : 'bar';
echo sprintf("#2 called the function %d times", $counter);

Outputs:

#1 called the function 1 times
#2 called the function 2 times

Demo.

Answer 2

return get_db_row($sql_parameters) ?: get_empty_row();

If you're running an earlier version of PHP that doesn't support this...

return ($x = get_db_row($sql_parameters)) ? $x : get_empty_row();

Should work just fine.