php - What's alternative of eval function?

Question

I use eval() in my current project like this:

if (class_exists($class_name)) //$class_name depends on user input
    eval($class_name.'::MyStaticMethod()');

eval() is executed if and only if class with the name $class_name exists so it's kinda safe, but I still don't think that this is the best solution.

Can I do the same what code above does without eval()?

Answer 1

I have recently answered this question. The last part of my answer perfectly answers this question and is much more useful for future readers than answers provided here. That's why I am answering my own question.

PHP has features that gives possibility to avoid using eval in most cases:

1. PHP is very dynamic language. It has ability to do following stuff with strings:

   • Define and/or get variable (supported from PHP 4.3). For example:

     $variableName = 'MyVariable';
     // Create new variable with the name defined in variable $variableName
     ${$variableName} = 'MyValue';
     //Outputs: string(7) "MyValue"
     var_dump($MyVariable);
     //Outputs: string(7) "MyValue"
     var_dump(${'MyVariable'});
     

     Demo

   • Call function (supported from PHP 4.3). For example:

     // Create function with the name defined in variable $functionName
     function MyFunction($argument) {
         return 'Argument passed is: '.$argument;
     }
     
     $functionName = 'MyFunction';
     
     // Outputs:
     // string(48) "Argument passed is: Calling MyFunction directly."
     var_dump(MyFunction('Calling MyFunction directly.'));
     // Outputs:
     // string(51) "Argument passed is: Calling MyFunction with string."
     var_dump($functionName('Calling MyFunction with string.'));
     

     Demo

   • Create instance of class (supported from PHP 5.0). For example:

     class MyClass {
         public function __construct() {
             echo 'Constructing MyClass'."
     ";
         }
     }
     
     $className = 'MyClass';
     
     $objFromString = new $className();
     // Outputs: object(MyClass)#1 (0) {}
     var_dump($objFromString);
     

     Demo

   • Call static method (supported from PHP 5.0). For example:

     class MyClass {
         public static function staticMethod() {
             return 'MyClass::staticMethod called';
         }
     }
     
     $staticMethodName = 'staticMethod';
     // Outputs: string(28) "MyClass::staticMethod called"
     var_dump(MyClass::$staticMethodName());
     

     Demo

     And from PHP 5.3 class name can also be defined by string. Example:

     class MyClass {
         public static function staticMethod() {
         return 'MyClass::staticMethod called';
         }
     }
     
     $className = 'MyClass';
     $staticMethodName = 'staticMethod';
     
     var_dump($className::$staticMethodName());
     var_dump($className::staticMethod());
     

     Demo

   • Call instance method of object (supported from PHP 5.0). For example:

     class MyClass {
         public function instanceMethod() {
             return 'MyClass::instanceMethod called';
         }
     }
     
     $methodName = 'instanceMethod';
     
     $obj = new MyClass();
     // Outputs: string(30) "MyClass::instanceMethod called"
     var_dump($obj->$methodName());
     

     Demo

   • Access static and instance properties of object (supported from PHP 5.0). For example:

     class MyClass {
         public static $myStaticProperty;
         public $myInstanceProperty;
     }
     
     $staticPropertyName = 'myStaticProperty';
     $instancePropertyName = 'myInstanceProperty';
     
     MyClass::${$staticPropertyName} = 'my static value';
     $obj = new MyClass();
     $obj->{$instancePropertyName} = 'my instance value';
     
     var_dump(MyClass::${$staticPropertyName});
     var_dump($obj->{$instancePropertyName});
     

     Demo

2. PHP has two functions: call_user_func and call_user_func_array for dynamic function/method calls. Both are perfectly documented so I won't go in details here.
3. Even if everything above is not enough PHP 5 comes with great Reflection API. Unfortunately, documentation has few examples but reflection is quite large topic to cover here. Basically, It's not a big deal to use reflection after reading how it works.