问题

I have created a class named calculator where I have set an arrow function as the property of the class. And I have passed that property to the init method. Once I run this program, It is not generated output. My expected output is 15. The code is below.

我已经创建了一个名为calculator的类，在这个类中，我将一个箭头函数设置为类的属性，并将该属性传递给了init方法。一旦运行这个程序，它没有生成输出。我期望的输出是15。以下是代码。

<?php
namespace Calculate;
class calculator{
    public $sum = fn(...$args) => array_sum($args);
    public function init(){
        return $this->sum(5, 10);
    }
}
$cal = new calculator();
print $cal->init(); // 期望的输出是15

But on the other hand, when I am putting the sum variable outside of the class and using it from the init method, It is working then. And it's providing the output 15. The code is below.

但另一方面，当我将sum变量放在类外部并在init方法中使用它时，它就可以正常工作了。并且它提供了输出为15的结果。以下是代码。

$sum = fn(...$args) => array_sum($args);
class calculator{
    public function init(){
        global $sum;
        return $sum(5, 10);
    }
}
$cal = new calculator();
print $cal->init(); // 输出是15

So, my question is can not I declare the arrow function as property or method of a class? If we can, what is the process, please?

所以，我的问题是我不能将箭头函数声明为类的属性或方法吗？如果可以的话，请问是什么过程？

<?php
namespace Calculate;
class calculator{
    public $sum = fn(...$args) => array_sum($args);
    public function init(){
        return $this->sum(5, 10);
    }
}
$cal = new calculator();
print $cal->init(); // Expected Output is 15

$sum = fn(...$args) => array_sum($args);
class calculator{
    public function init(){
        global $sum;
        return $sum(5, 10);
    }
}
$cal = new calculator();
print $cal->init(); // Output is 15

答案1

得分: 2

First, the arrow function should be assigned to a variable, not a class property. Arrow functions in PHP cannot be directly assigned as class properties. Instead, you can define a regular method that uses the arrow function internally. Here's an updated version of the code:

namespace Calculate;
class Calculator {
    private $sum;
    public function __construct() {
        $this->sum = fn(...$args) => array_sum($args);
    }
    public function init() {
        return ($this->sum)(5, 10);
    }
}
$cal = new Calculator();
echo $cal->init(); // Output: 15

Now, when you run the code, it will correctly output 15, which is the expected result.

namespace Calculate;
class Calculator {
    private $sum;
    public function __construct() {
        $this->sum = fn(...$args) => array_sum($args);
    }
    public function init() {
        return ($this->sum)(5, 10);
    }
}
$cal = new Calculator();
echo $cal->init(); // Output: 15