How to call arrow function inside another function in php

Question

How i can use arrow or anonymous function like this in php or something similar syntax to achieve this.

class calculator{
  // $sum = fn(...$args) => array_sum($args);
  public function hello(){
     // $sum(5, 10)
  }
}

or this way

$sum = fn(...$args) => array_sum($args);
class calculator{
  public function hello(){
     // $sum(5, 10)
  }
}

Answer 1

An arrow function in PHP is not a special kind of function, just a convenient syntax for declaring an "anonymous function" or "closure" - that is, a function which you can pass around as a normal variable.

So once you create your anonymous function $sum, it is just like any other variable - you have to pass that variable to where you need it. Normally, this is done so that you can change which function gets called by passing different functions in - think of something like registering an error handler, for instance.

Your first example is not legal PHP, because you can't declare a variable floating around in a class like that. Your second example is valid syntax, but the variable $sum has not been passed into the function, so doesn't exist there. A working (but not very useful) example would be this:

$sum = fn(...$args) => array_sum($args);
class calculator{
  public function hello(callable $functionToCall){
     echo $functionToCall(5, 10);
  }
}
$calc = new calculator();
$calc->hello($sum);

If all you're looking for is to add a sum method to the class, you don't need arrow syntax at all:

class calculator{
  public function sum(...$args) {
     return array_sum($args);
  }
}

Similarly, if all you want is a function named sum available everywhere, just declare it as a normal function, not a closure:

function sum(...$args) {
    return array_sum($args);
}
class calculator {
    public function hello() {
       echo sum(5, 10);
   }
}