PHP单例类的最佳实践[重复]

Question

Possible Duplicate:
Who needs singletons?

I always write with respect to best practice, but I also want to understand why a given thing is a best practice.

I've read on in an article (I unfortunately don't remember) that singleton classes are prefered to be instantiated, rather than being made with static functions and accessed with the scope resolution operator (::). So if I have a class that contains all my tools to validate, in short:

class validate {
    private function __construct(){}
    public static function email($input){
        return true;
    }
}

I've been told this is considered bad practice (or at least warned against), because of such things as the garbage collector and maintenance. So what the critiques of the "singleton class as static methods" wants, is that I instantiate a class I'm 100% certain I will only ever instantiate once. To me it seems like doing "double work", because it's all ready there. What am I missing?

What's the view on the matter? Of course it's not a life and death issue, but one might as well do a thing the right way, if the option is there :)

Answer 1

An example singleton classes in php:
Creating the Singleton design pattern in PHP5 : Ans 1 :
Creating the Singleton design pattern in PHP5 : Ans 2 :

Singleton is considered "bad practice".

Mainly because of this: How is testing the registry pattern or singleton hard in PHP?

• why are singleton bad?

• why singletons are evil?

• A good approach: Dependency Injection

• Presentation on reusability: Decouple your PHP code for reusability

• Do you need a dependency injection container

• Static methods vs singletons choose neither

• The Clean Code Talks - "Global State and Singletons"

• Inversion of Control Containers and the Dependency Injection pattern

Wanna read more? :

• What are the disadvantages of using a PHP database class as a singleton?

• Database abstraction class design using PHP PDO

• Would singleton be a good design pattern for a microblogging site?

• Modifying a class to encapsulate instead of inherit

• How to access an object from another class?

• Testing Code That Uses Singletons

A Singleton decision diagram (source):