使用PHP 5.4构建Singleton特性 [英] Building a Singleton Trait with PHP 5.4

问题描述

我们最近讨论了是否有可能构建trait Singleton Singletons have very little - if not to say no - use in PHP 和> one should 'just create one' > ，但仅用于探索特质的可能性:

<?php
trait Singleton
{
    protected static $instance;
    final public static function getInstance()
    {
        return isset(static::$instance)
            ? static::$instance
            : static::$instance = new static;
    }
    final private function __construct() {
        static::init();
    }
    protected function init() {}
    final private function __wakeup() {}
    final private function __clone() {}    
}

class A  {
    use Singleton;
    public function __construct() {
        echo "Doesn't work out!";
    }
}

$a = new A(); // Works fine

复制: http://codepad.viper-7.com/NmP0nZ

问题是:可以用PHP创建Singleton Trait吗?

解决方案

我们找到了快速解决方案(感谢聊天！):

如果一个特征和一个类都定义了相同的方法，则使用一个类(如果使用的话)

因此，仅当使用Singleton特质的类未定义__construct()

时，Singleton特质才有效

特质:

<?php
trait Singleton
{
    protected static $instance;
    final public static function getInstance()
    {
        return isset(static::$instance)
            ? static::$instance
            : static::$instance = new static;
    }
    final private function __construct() {
        $this->init();
    }
    protected function init() {}
    final private function __wakeup() {}
    final private function __clone() {}    
}

消费类示例:

<?php    
class A  {
    use Singleton;

    protected function init() {
        $this->foo = 1;
        echo "Hi!\n";
    }
}

var_dump(A::getInstance());

new A();

var_dump现在会产生预期的输出:

Hi!
object(A)#1 (1) {
  ["foo"]=>
  int(1)
}

，新的失败:

Fatal error: Call to private A::__construct() from invalid context in ...

---

Demo

We recently had a discussion if it was possible to build a trait Singleton PHP Traits and we played around with it a possible Implementation but ran into issues with building one.

This is an academic exercise. I know that Singletons have very little - if not to say no - use in PHP and that one should 'just create one' but just for exploring the possibilities of traits:

<?php
trait Singleton
{
    protected static $instance;
    final public static function getInstance()
    {
        return isset(static::$instance)
            ? static::$instance
            : static::$instance = new static;
    }
    final private function __construct() {
        static::init();
    }
    protected function init() {}
    final private function __wakeup() {}
    final private function __clone() {}    
}

class A  {
    use Singleton;
    public function __construct() {
        echo "Doesn't work out!";
    }
}

$a = new A(); // Works fine

reproduce: http://codepad.viper-7.com/NmP0nZ

The question is: It is possible to create a Singleton Trait in PHP?

解决方案

Quick solution we've found (thanks chat!):

If a trait and a class both define the same method, the one of class if used

So the Singleton trait only works if the class that uses it doesn't define a __construct()

Trait:

<?php
trait Singleton
{
    protected static $instance;
    final public static function getInstance()
    {
        return isset(static::$instance)
            ? static::$instance
            : static::$instance = new static;
    }
    final private function __construct() {
        $this->init();
    }
    protected function init() {}
    final private function __wakeup() {}
    final private function __clone() {}    
}

Example for a consuming class:

<?php    
class A  {
    use Singleton;

    protected function init() {
        $this->foo = 1;
        echo "Hi!\n";
    }
}

var_dump(A::getInstance());

new A();

The var_dump now produces the expected output:

Hi!
object(A)#1 (1) {
  ["foo"]=>
  int(1)
}

and the new fails:

Fatal error: Call to private A::__construct() from invalid context in ...

---

Demo

这篇关于使用PHP 5.4构建Singleton特性的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！