Detailed explanation of how to implement overloading examples of functions and constructors in PHP

Since PHP is a weakly typed language, the input parameter type of the function cannot be determined (type hints can be used, but type hints cannot be used for integer types, strings and other scalar types), and for a function, for example, only 3 input parameters are defined, but PHP inputs 4 or more parameters when calling. Therefore, based on these two points, it is destined that functions cannot be overloaded in PHP (similar to Javascript languages), and there cannot be constructors of overloading.

Since implementing function overloading is very helpful to improve development efficiency, it would be great if it could be like C# or C++. In fact, PHP provides a magic method, mixed call (string name, array arguments). This method is also mentioned in the php manual. According to the official documentation, it is said that this method can achieve function overloading. When calling a method that does not exist in the object, if the call() method is defined, the method will be called. For example, the following code:

<?php
class A
{
   function call ( $name, $arguments )
    {
        echo "call调用<br/>";
        echo &#39;$name为&#39;.$name."<br/>";
        print_r ($arguments);
    }
}
(new A)->test("test","argument");
?>

The running result is:

call call

$name is test

Array ( [0] => test [ 1] => argument )

So you only need to use this magic method to achieve function overloading.

The code is as follows:

<?php
class A
{
     function call ($name, $args )
    {
        if($name==&#39;f&#39;)
        {
            $i=count($args);
            if (method_exists($this,$f=&#39;f&#39;.$i)) {
                call_user_func_array(array($this,$f),$args);
            }
        }
    }
    function f1($a1)
    {
        echo "1个参数".$a1."<br/>";
    }
    function f2($a1,$a2)
    {
        echo "2个参数".$a1.",".$a2."<br/>";
    }
    function f3($a1,$a2,$a3)
    {
          echo "3个参数".$a1.",".$a2.",".$a3."<br/>";
    }
}
(new A)->f(&#39;a&#39;);
(new A)->f(&#39;a&#39;,&#39;b&#39;);
(new A)->f(&#39;a&#39;,&#39;b&#39;,&#39;c&#39;);
输出如下：
1个参数a   2个参数a,b    3个参数a,b,c

Similarly, in PHP, overloading of constructors can only be implemented in a flexible way. The key element of implementation is to obtain input parameters and determine which method to call based on the input parameters. The following is a sample code:

<?php
class A
{
    function construct()
    {
        echo "执行构造函数<br/>";
$a = func_get_args(); //获取构造函数中的参数
        $i = count($a);
        if (method_exists($this,$f=&#39;construct&#39;.$i)) {
call_user_func_array(array($this,$f),$a);
        }
    }
    function construct1($a1)
    {
        echo "1个参数".$a1."<br/>";
    }
    function construct2($a1,$a2)
    {
        echo "2个参数".$a1.",".$a2."<br/>";
    }
function construct3($a1,$a2,$a3)
    {
          echo "3个参数".$a1.",".$a2.",".$a3."<br/>";
    }
}
$o = new A(&#39;a&#39;);
$o = new A(&#39;a&#39;,&#39;b&#39;);
$o = new A(&#39;a&#39;,&#39;b&#39;,&#39;c&#39;);
?>

Execute the constructor
1 parameter a
Execute the constructor
2 parameters a,b
Execute the constructor
3 parameters a, b, c

By the way, just like C# and other object-oriented languages, in PHP, if the constructor is set to private or protected, the object cannot be instantiated.

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