将elses转换为具有布尔返回值的开关

I am trying to convert this simple set of else statement into a more easily readable switch;

$parts_arr = explode('.', $_SERVER['SERVER_NAME']);

if (in_array('dev', $parts_arr)) {
    DEFINE('APP_ENV', "dev");
} else if (in_array('staging', $parts_arr)) {
    DEFINE('APP_ENV', "staging");
} else if (in_array('local', $parts_arr)) {
    DEFINE('APP_ENV', "local");
} else {
    DEFINE('APP_ENV', "live");
}

However I have completely drawn a blank. I can't use a foreach loop and use the string as the case as APP_ENV cannot be redefined.

You can't turn it into switch-case structure unless you're doing string comparaison.

Maybe something like this :

$str = array_pop(explode('.', $_SERVER['SERVER_NAME']));

switch($str)
{
   case 'dev' :
      DEFINE('APP_ENV', "dev");
   break;
   // en so on
}

Sunil Pachlangia's solution won't work because he is comparing an array and a string

You may only check the whole server name.

switch($_SERVER['SERVER_NAME']) {
    case 'mysite.com':
    case 'www.mysite.com':
      DEFINE('APP_ENV', "live");
      break;
    case 'dev.mysite.com':
      DEFINE('APP_ENV', "dev");
      break;
    case 'staging.mysite.com':
      DEFINE('APP_ENV', "staging");
      break;
    case 'mylocalhost.local':
      DEFINE('APP_ENV', "local");
      break;
    default:
      exit;
}

<?php

$parts_arr = explode('.', $_SERVER['SERVER_NAME']);
switch (true) {
    case in_array('dev', $parts_arr):
        DEFINE('APP_ENV', "dev");
        break;
    case in_array('staging', $parts_arr):
        DEFINE('APP_ENV', "staging");
        break;
    case in_array('local', $parts_arr):
        DEFINE('APP_ENV', "local");
        break;
    default:
        DEFINE('APP_ENV', "live");
        break;
}

I think I'd tend to shy away from splitting strings and analysing array elements, as @Almo-Do commented Be specific in some kind of config file.

$environments = array(
  'localhost' = > 'local'
, 'staging.mysite.com' > 'staging'
// etc - see? now you can comment some out
//, 'mysite.com' => 'live'
);

Then simply

define ('APP_ENV', $environments[$_SERVER['SERVER_NAME']]);

Or even be a bit more defensive prior to that, something like :

if (!array_key_exists($environments[$_SERVER['SERVER_NAME'])) die('suitable msg');