Stacking Multiple Ternary Operators in PHP

This is what I wrote :

 $Myprovince = (
($province == 6) ? "city-1" :
($province == 7) ? "city-2" :
($province == 8) ? "city-3开发者_如何学C" :
($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?

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

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';

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 = ...) {
   ...
}

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.

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"

Try with some more parenthesis :

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

Your code has a problem with the ternary operator priority.

But I think you should really drop this operator and try to use a switch instead.

I think the more readable way to write nested ternary operators in PHP is like this:

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

All you need to do is count the number of opening parenthesis (() and add the same number of closing parenthesis ()) at the end of the last line.

Another option is to use one-line if/elseif/else, as already suggested - however, I would format them visually like this for even more readability:

if      ($province == 6)  $myprovince = "city-1";
elseif  ($province == 7)  $myprovince = "city-2";
elseif  ($province == 8)  $myprovince = "city-3";
elseif  ($province == 30) $myprovince = "city-4";
else                      $myprovince = "out of borders";

I got myself into the same problem today. The others already giving acceptable solutions. Mine just an emphasis to one liner ifs. More readable in my opinion.

if ($province == 6) $Myprovince = 'city-1';
elseif ($province == 7) $Myprovince = 'city-2';
elseif ($province == 8) $Myprovince = 'city-3';
elseif ($province == 30) $Myprovince = 'city-4';
else $Myprovince = 'out of borders';

Another solution for this was introduced with the match statement in PHP 8:

$Myprovince = match ($province) {
    6 => "city-1",
    7 => "city-2",
    8 => "city-3",
    30 => "city-4",
    default => "out of borders",
};

It's essentially just a less-verbose switch statement that's ideal for simple assignment. Multiple conditions can be added as well:

$Myprovince = match ($province) {
    4, 5, 6 => "city-1",
    7, 9, 10 => "city-2",
    8 => "city-3",
    30 => "city-4",
    default => "out of borders",
};

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';
}

In this type of case I always recommend to use switch case syntax. As you said it's experimental so here is the code you need to use:

$province = 9;
$Myprovince = $province == 6 ? "city-1" : (
    $province == 7 ? "city-2" : (
        $province == 8 ? "city-3" : (
            $province == 9 ? "city-4" : "out of border"
        )
    )
);
echo $Myprovince;

The output will be:

out of border because the $province is = 9

Again I recommend to use switch case. Below the code:

switch ($province) {
    case 6:
        $Myprovince = 'city-1';
        break;
    case 7:
        $Myprovince = 'city-2';
        break;
    case 8:
        $Myprovince = 'city-3';
        break;
    case 9:
        $Myprovince = 'city-4';
        break;
    default:
        $Myprovince = 'out of borders';
}

There is some other Ternary Operators that we can use in PHP

The shorthand ternary operator

$result = $initial ?: 'default';

In this case, the value of $result will be the value of $initial, unless $initial evaluates to false, in which case the string 'default' is used.

Chaining Ternary Operators

We already used this type of ternary operators in our above code.

Null Coalescing Operator

t similar to the ternary operator, but will behave like isset on the lefthand operand instead of just using its boolean value. This makes this operator especially useful for arrays and assigning defaults when a variable is not set.

$undefined ?? 'fallback'; // 'fallback'

Because of $underfined variable the output will be fallback

$assigned = 'foo';
$assigned ?? 'fallback'; // 'foo'

The $assigned has a value now so the output will be "foo"

Another Great Example

You can use something like below in PHP.

$output = $truthy && 'The output here';
echo $output; // The output here

Please note the &&