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Pseudotypes and pseudovariables in PHP

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Release： 2023-03-10 20:00:01

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1. Pseudo-types

There are three PHP pseudo-types, namely: 1, mixed type. 2. number digital type. 3. callbackCallback type.

1, mixed mixed type:

mixed indicates that a parameter can accept multiple different types, but not all types.

2, number numeric type:

The number parameter can accept integer integer type and floatFloating point type.

3, callback type:

For example, the call_user_func() function can receive a user-defined function as a parameter, which is php A built-in function. The callback function can not only be a function, but also a method of an object and a method of a static class. A php function is passed using the function namestring. Any built-in or user-defined function can be passed, except language structures such as array(), echo(), empty() ,eval(),exit(),isset(),list(),print(),unset(), etc.

If you want to pass in the method of an object, it needs to be passed in the form of an array. The array subscript 0 is the object name and the subscript 1 is the method name. If there is no static class instantiated as an object, to pass its method, replace the object name specified by the array 0 subscript with the name of the class.

In addition to ordinary user-defined functions, you can also use create_function to create an anonymous callback function.

Example::

<?php

	//普通的回调函数
	function my_callback_function(){
		echo "my is callback function.";
	}

	//回调方法
	class MyClass{
		static function myCallbackMethod(){
			echo "my is callback method.";
		}
	}

	//num1:回调函数
	call_user_func(&#39;my_callback_function&#39;);

	//num2:静态类的方法
	call_user_func(array(&#39;MyClass&#39;,&#39;myCallbackMethod&#39;));

	//num3:对象方法
	$obj = new MyClass();
	call_user_func(array($obj,&#39;myCallbackMethod&#39;));

	//num4:静态类的方法（5.3.0以上）
	call_user_func(&#39;MyClass::myCallbackMethod&#39;);

	//num5:相对静态方法调用
	class A {
		public static function who(){
			echo "A";
		}
	}

	class B extends A {
		public static function who(){
			echo "B";
		}
	}

	call_user_func(array(&#39;B&#39;,&#39;parent::who&#39;));	//输出B

	//num6:调用时传入参数
	function test($a,$b){
		echo $a;
		echo $b;
	}

	call_user_function(&#39;test&#39;,&#39;1&#39;,&#39;2&#39;);	//输出1 2

	//num7:调用类方法传入参数
	class a(){
		function b($c){
			echo $c;
		}
	}

	call_user_func(array(&#39;a&#39;,&#39;b&#39;),&#39;1&#39;);	//输出1

	//num8:call_user_func_array与call_user_func很相似，只不过换了一种方式传递参数，让参数结构更清晰：
	function a($b,$c){
		echo $b;
		echo $c;
	}

	call_user_func_array(&#39;a&#39;,array(&#39;1&#39;,&#39;2&#39;));	//输出1 2

	//num9:用call_user_func_array调用类内部方法
	class A(){
		function a($b,$c){
			echo $b;
			echo $c;
		}
	}
	
	call_user_func_array(array(&#39;A&#39;,&#39;a&#39;),array(&#39;1&#39;,&#39;2&#39;));	//输出1 2

	//num10:call_user_func函数和call_user_func_array函数都支持引用，这让他们和普通的函数调用更趋于功能一致：
	function a($b){
		$b++;
	}
	$c=0;
	call_user_func(&#39;a&#39;,$c);	//输出1
	call_user_func(&#39;a&#39;,array($c));	//输出2

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2. Pseudo variables

$... in php is pseudo Variable means etc. This variable name is used when a function can accept any number of parameters.

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