How to write multiple expressions in PHP arrow functions

Question

How do you write a PHP arrow function with multiple line expressions?

JavaScript one-liner example:

const dob = (age) => 2021 - age;

PHP one-liner equivalent:

$dob = fn($age) => 2021 - $age;

Javascript multiple line example:

const dob = (age) => {
    if (!age) {
        return null;
    }
    const new_age = 2021 - age; 
    console.log("Your new age is " + new_age);
    return new_age;
}

What is the PHP equivalent for multiple lines within an arrow function?

Theresatherese

What exactly are you asking? Just how to put the expression on a separate line, or to have multiple expressions? In PHP, you can only have one expression, but you can write it in multiple lines (as long as it's just a single expression, like your example of "multiple lines") – Sophisticated

@MagnusEriksson I'm asking how to put multiple expressions or lines of code in an arrow function. I updated my question. If you understand the idea of an arrow function it will help – Theresatherese

I wish it was possible with PHP, but it's not. Only one line (expression) is allowed there. – Hanover

The JavaScript example here is very god, I've came here as I was wondering how to log arrow function calls... Seems impossible. – Alcohol

Answer 1

Arrow functions in PHP have the form fn (argument_list) => expr. You can only have a single expression in the body of the function.

You can write the expression over multiple lines without problem:

fn($age) =>
      $age
    ? 2021 - $age
    : null

If you really need multiple expressions, then you can simply use anonymous function. The closures aren't automatic as they are with arrow functions, but if you don't need it, it gives exactly the same result.

$dob = function ($age) {
    if (!$age) { return null; }
    $new_age = 2021 - ^$age; 
    echo "Your new age is ". $new_age;

    return $new_age;
}

Braxy

This is still a single expression and not multiple. I updated my question. – Theresatherese

@EmekaMbah I thought the first line of my answer was pretty clear: you can't have more than a single expression in the body of an arrow function in PHP. Just use a standard function for that. – Braxy

Ok. Got it. Do you know if PHP plan to make this possible since single expression is not usually the case – Theresatherese

@EmekaMbah No, I haven't seen any RFC about this. But that's really not needed, especially if you don't need any capture like in your updated question: function ($age) { … } does the same thing than your JavaScript example. – Braxy

Answer 2

The usage of multiple expressions is not allowed, according to the RFC. It covers the assignment of only a single expression. The extension is discussed further down in the RFC, but not implemented

Amphora

Answer 3

There was some discussion in the PHP Internals mailing list regarding possible syntactic options for introducing the brevity and and data accessibility benefits of multiline arrow functions, but nothing gathered sufficient community support.

Until progress is made on that topic, your multi-line snippet can be written with a conditionally nested Immediately Invoked Functional Expression. My snippet will leverage the fact that when the passed-in age is not null, the returned value is expected to be an integer and it is therefore safe to multiply the calculated value by 1 (the return value of print). Otherwise,

Code: (Demo)

$name = 'mickmackusa';

$dob = fn(?int $age): ?int => !$age
    ? null
    : (
          fn($newAge) => $newAge * print "$name's age is $newAge\n" 
      )(2021 - $age);

var_export($dob(null));
echo "\n---\n";
var_export($dob(31));

Output:

NULL
---
mickmackusa's age is 1990
1990

Alternatively, use another ternary condition instead of multiplying.

Instal

Answer 4

$getSquare = fn($num) => (function ($temp){
    echo "The square of $temp is : ";
    return $temp**2;
})($num);
echo $getSquare(10);

Arianna

Then why even bother with arrow function here? ;) – Sulphuric

@Sulphuric Its a hack for writing miltiline expression just like what we do in Javascript. This will also be helpful in match expression (newer version of switch case) – Arianna

Answer 5

You can use something like (expr1) && (expr2), for example:

$f = fn () => ($hasChanges = true) && ($this->comment = $operation->comment)

Note that expr1 must be true in any case, otherwise expr2 will not be executed.

If expr1 returns nothing (void) or falsy value, then wrap expr1 to (expr1 || true).

Kr

The arrow function will return the boolean result of the evaluation, so this is not appropriate for the asked question. – Instal