PHP オブジェクト指向の __tostring() と __invoke() の詳細なコード例

<?php
ini_set(&#39;display_errors&#39;, 1);
class A{
    public $name;    
    public $age;   
     public $sex;    
     function construct($name, $age, $sex){
        $this->name = $name;        
        $this->age = $age;        
        $this->sex = $sex;   
    }
}
$obj1 = new A(&#39;张三&#39;, 15, &#39;男&#39;);
echo $obj1;    //echo 后面为字符串，而对象不是字符串，会报错
$v1 = "abc" . $obj1;  //.为字符串连接符，会报错
$v2 = "abx" + $obj1;  //+为加法运算符，会报错?>

Catchable fatal error: Object of class A could not be converted to string
Catchable fatal error: Object of class A could not be converted to string
Notice: Object of class A could not be converted to int

<?php
ini_set(&#39;display_errors&#39;, 1);
class A{
    public $name;    
    public $age;    
    public $sex;    
    function construct($name, $age, $sex){
        $this->name = $name;        
        $this->age = $age;        
        $this->sex = $sex;   
    }    function tostring(){
        $str = "姓名：" . $this->name;   
        $str .= "年龄：" . $this->age;    
        $str .= "，性别：" . $this->sex;        
        return $str;   //这里可以返回“任何字符串内容”

    }
}
$obj1 = new A(&#39;张三&#39;, 15, &#39;男&#39;);
echo $obj1;    //调用tostring(),不会报错?>

姓名：张三年龄：15，性别：男