PHP ideal way to check function returns true

Question

Which of the following way of checking whether a function returns TRUE or FALSE is best, in terms of efficiency and code readability?

I was told by a friend that Method B is a good practice, but I believe Method A is better since it checks whether function returns TRUE then assigns.

Method A: (Checks whether function is TRUE and then assigns.)

if ($result = $db->getResults($id)) {
    echo $result;
} else {
    echo 'fail';
}

Method B: (First assigns the value, then checks—two operations.)

$result = $db->getResults(90);
if ($result) {
    echo $result;
} else {
    echo 'fail';
}

---

public function getResults($no) {
    if ($no > 85) {
        $result = 'pass';
        return $result;
    } else {
       return FALSE;
    }
}

Answer 1

Actually, both methods assign the value first before comparing its value. Therefore, in terms of efficiency, there's no difference.

For code readability, you could write extra parentheses around the assignment if you choose method A. Method B has a slight advantage when you have to perform debugging before the branch, i.e.:

$res = $db->getResult(95);
var_dump($res); // added for debugging without having to move the code out of the condition
echo $res ? $res : 'fail';

The ternary operator I've used above is yet another way to do your branching; its efficiency is in the same ballpark though. Since the variable itself is used solely in the truthy branch you can also use the shortened ternary operator (>= 5.3) like so:

echo $res ?: 'fail';

Although ternary operators are a powerful concept, they're easy to abuse as well and can cause either bugs or a WTF during code review. My personal guideline is to start favouring an if/else construct when either the condition has multiple sub-expressions or when the manual is opened under operator precedence.

Answer 2

The performance difference is irrelevant; it is really minor (if not zero) and if such minor differences mattered not using PHP at all would be the only proper solution.

Since you only need the variable in the true-branch of the if statement and it's likely to be something other than just a plain true using if(($foo = bar())) (with the additional parentheses to indicate that it's not supposed to be ==) is the cleanest way - but opinions on that will most likely vary.

Answer 3

if(!$result = $db->getResult($id)){
    echo 'fail';
}else{
    echo $result;
}

Why do you test against false first and true second? Because, if this is in a function, you may want to choose the easy way out. Like this:

if(!$result = $db->getResult($id)){
    echo 'fail';
    // It failed, it's over... so bail here quickly.
    return false;
}
// We succeeded, continue heavy processing of result
// without being contained in a cumbersome block.
echo $result;

There's no right or wrong way. It's always a choice of design. Do you need to return a false in case of failure, try for false first and return or... continue processing in the main block of the function if it succeeded.

Do remember that PHP is very lax regarding stuff like this. It's always easier and more clear to create variables in place right inside the if. Shorter clean code is easier to read code:

if(($result = $db->getResult($id)) === true){
    // true
}else if($result === false){
    // false
}else{
    // not a bool :) handle it
}

Hope I made sense.