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The PHP wiki has a great developer walkthrough of the hows and whys of the new lambda in PHP 5.3. I’ve been digging around for something like this for a while. There are some important distinctions about the way PHP lambdas work, especially if you’re used to closures in languages like JavaScript.

Highlights:

• Lambdas do not automatically inherit surrounding scope. You must specify the variables you want to be available to the method:

$foo = 1;
      $bar = function() use($foo) {
          echo "$foo\n";
      };

• Lambdas cannot be invoked directly when assigned to an object property:

$foo = new stdClass();
      $foo->bar = function() {
          echo "hello, world!\n";
      };
      $foo->bar(); // will trigger an error

      // assign it to a temporary variable instead
      $bar = $foo->bar;
      $bar();

• Lambdas will throw an error when serialized
• Lambdas have no $this scope