Julien Cambien

Arrow functions in PHP were an awesome addition and I would not work without it today. I wish we had the multi-line version.

I think complaints about the syntax being messy are really about the array manipulation functions being inherently hard to format nicely.

To be clear I agree that the proposed example isn't great, nested closures are never going to win any readabillity prizes. If however we look at any non-array based manipulation I think the readabillity is objectively better:

$name = 'my_user_name'
    |> fn (string $string): string => str_replace('_', ' ', $string)
    |> strtolower(...)
    |> ucwords(...)
    |> trim(...);

Or without first class callables:

$name = 'my_user_name'
    |> fn (string $string): string => str_replace('_', ' ', $string)
    |> fn (string $string): string => strtolower($string)
    |> fn (string $string): string => ucwords($string)
    |> fn (string $string): string => trim($string);

Bonus: this also adds runtime type checks to each step. Eg strreplace returns string|array

I can't imagine anyone would think this is better:

$name = trim(
    ucwords(
        strtolower(
            str_replace('_', ' ', 'my_user_name')
        )
    )
);

With First-class callable syntax available since 8.1, it would now be possible to write it as below, which is much better then string names of functions:

$result = "Hello World"
    |> htmlentities(...)
    |> str_split(...)
    |> fn($x) => array_map(strtoupper(...), $x)
    |> fn($x) => array_filter($x, fn($v) => $v != 'O');