How to limit variable to a local scope?

Question

Is it possible to do something similar to the using keyword in C# (and probably others) to limit variable scope? I'm experimenting with database connection patterns, and am currently trying to get this to work:

$db = array(
    "server"   =>"localhost",
    "user"     =>"root",
    "pass"     =>"my_password",
    "database" =>"my_database"
);

$pdo = null;

{  // ???  These seem to be completely ignored, no errors, no effect at all
    extract($db);
    $pdo = new PDO("mysql:host=$server;dbname=$database", $user, $pass);
}

//Do database stuff

I'm using extract, which is normally a bad idea, so I'm trying to protect whatever it returns where those curly braces are. In C# I could probably do something like using (extract($db)) { ... } and whatever extract returns would be limited to that scope, but I can't figure out if this is possible in PHP. I'm not even sure if PHP disposes of variables.

Answer 1

Instead of code blocks, IIFEs, or "Immediately invoked function expressions" could be used in PHP too if necessary – they're not just for JavaScript:
https://en.wikipedia.org/wiki/Immediately_invoked_function_expression

$x = 1;  // global var
$y = 2;  // global var
echo "x={$x}, y={$y}\n";

// PHP 5.3+
call_user_func(function()use( & $x ){
  $x = 33;  // reference to the global var because use( & $x )
  $y = 44;  // local var
  echo "x={$x}, y={$y}\n";
});

// PHP 7+
(function()use( & $x ){
  $x = 555;  // reference to the global var because use( & $x )
  $y = 666;  // local var
  echo "x={$x}, y={$y}\n";
})();

echo "x={$x}, y={$y}\n";

Output:

x=1,   y=2    // initial global var values
x=33,  y=44   // inside the first PHP5.3+ iife
x=555, y=666  // inside the second PHP7+ iife
x=555, y=2    // the global variables after executing both

Answer 2

Since PHP >= 5.3 you can use Namespaces like this:

// per file
namespace App\One
$var = 1;

// or, per block
namespace App\Two {
    $var = 2;
}

Then later you can call it like this -- there are other ways as well:

echo \App\Two\var;

Update

Well, it seems that variables are not affected by namespace.

Although any valid PHP code can be contained within a namespace, only the following types of code are affected by namespaces: classes (including abstracts and traits), interfaces, functions and constants.

source

But what you can still do is to use Constants instead:

namespace App\One;
define('App\One\ABC', 'abc');            // specified namespace
define(__NAMESPACE__ . '\XYZ', 'xyz');   // current namespace -- which is App\One here