Stacking Multiple Ternary Operators in PHP

Question

This is what I wrote :

 $Myprovince = (
($province == 6) ? "city-1" :
($province == 7) ? "city-2" :
($province == 8) ? "city-3" :
($province == 30) ? "city-4" : "out of borders"
);

But for every field I got the value city-4. I want to use ternary operators instead of switch/if because I want to experiment and see how it would be done.

What's the problem with this code?

Answer 1

Don't abuse the ternary operator for that sort of thing. It makes debugging near impossible to follow. Why not do something like

switch($province) {
    case 6: $Myprovince = "city-1"; break;
    case 7: ...
}

or simply some chained if/then/else

if ($province == 6) {
     $Myprovince = "city-1";
} elseif ($province = ...) {
   ...
}

Answer 2

Some people have suggested using a switch statement or an if/else statement. But I would use an array instead, to make it easier to maintain and easier to read:

$provinces = array (
    6 => 'city-1',
    7 => 'city-2',
    8 => 'city-3',
    30 => 'city-4'
);

// then you can call:

$Myprovince = isset($provinces[$province]) ? $provinces[$province] : 'out of borders';

Why?

The code will probably eventually be easier to manage. Maybe you'll want to add those province-to-city mappings from database one day.. etc.. That will be hard to maintain with a bunch of switch/case statements.

Answer 3

I understand this is a question about PHP, but since this is just an educational exercise anyways I thought you might be interested in learning that Ruby and Javascript actually behave the way you expect.

Ruby:

ree-1.8.7-2012.02 :009 > def foo x
ree-1.8.7-2012.02 :010?>   x == 1 ? "city 1" : x == 2 ? "city 2" : "out of borders"
ree-1.8.7-2012.02 :011?>   end
 => nil
ree-1.8.7-2012.02 :012 > foo 1
 => "city 1"
ree-1.8.7-2012.02 :013 > foo 2
 => "city 2"
ree-1.8.7-2012.02 :014 > foo 3
 => "out of borders"

Javascript:

> function f(x) { return x == 1 ? "city 1" : x == 2 ? "city 2" : "out of borders"; }
undefined
> f(1)
"city 1"
> f(2)
"city 2"
> f(3)
"out of borders"

Answer 4

Others have already suggested the right way of doing it but if you really want to use ternary operator you need to use parenthesis as:

$province = 7;
 $Myprovince = (
 ($province == 6) ? "city-1" :
  (($province == 7) ? "city-2" :
   (($province == 8) ? "city-3" :
    (($province == 30) ? "city-4" : "out of borders")))
 );

Updated Link

Answer 5

The ternary operator is evaluated from left to right. So if you don't group the expressions properly, you will get an unexpected result.

PHP's advice is ^[docs]:

It is recommended that you avoid "stacking" ternary expressions. PHP's behaviour when using more than one ternary operator within a single statement is non-obvious.

Your code actually is evaluated as:

(
    (
        (
            $province == 6 ? "city-1" : $province == 7
        ) ? "city-2" : 
        $province == 8
    ) ? "city-3" : $province == 30
) ? "city-4" : "out of borders";

where it should be

$province == 6 ? "city-1" : (
    $province == 7 ? "city-2" : (
        $province == 8 ? "city-3" : (
           $province == 30 ? "city-4" : "out of borders"
        )
    )
);

This code might look fine but someone will read it and they will need more time than they should to understand what this code is doing.

---

You would be better off with something like this:

$map = array( 6 = >'city-1', 
              7 => 'city-2', 
              8 => 'city-3', 
             30 => 'city-4');

$Myprovince = "out of borders";

if(array_key_exists($province, $map)) {
    $Myprovince = $map[$province];
}

Or as @Jonah mentioned in his comment:

$Myprovince = isset($map[$province]) ? $map[$province] : 'out of borders';

Answer 6

Use switch instead. Ternary operators really shouldn't be used for more than single conditions, as they quickly become very difficult to understand.

switch ($province) {
    case 6:
        $Myprovince = 'city-1';
        break;
    case 7:
        $Myprovince = 'city-2';
        break;
    case 8:
        $Myprovince = 'city-3';
        break;
    case 30:
        $Myprovince = 'city-4';
        break;
    default:
        $Myprovince = 'out of borders';
}