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Thread-Topic: [PHP-DEV] Re: Adding `final class Deque` to PHP
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Date: Wed, 2 Feb 2022 14:59:42 +0000
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Subject: Re: [PHP-DEV] Re: Adding `final class Deque` to PHP
From: tysonandre775@hotmail.com (tyson andre)

Hi Larry Garfield,=0A=
=0A=
> Request:=0A=
>=0A=
> push() and unshift() currently return void.  That's not helpful.  It woul=
d be vastly more useful if they both returned $this.  Not as much for chain=
ing, but more so that you can add a value to a queue and pass it as an argu=
ment to another call (often recursive, but not necessarily) in a single ope=
ration.=0A=
>=0A=
> Example: I was doing last year's Advent of Code in functional PHP, and ha=
d a stack walker that looked like this:=0A=
>=0A=
> function parse(string $line, $pos =3D 0, array $stack =3D []): Result|str=
ing=0A=
> {=0A=
>     $next =3D $line[$pos] ?? null;=0A=
>     $head =3D $stack[0] ?? null;=0A=
>=0A=
>     return match ($next) {=0A=
>         // Opening brace, push an "expected" onto the stack.=0A=
>         '{' =3D> parse($line, $pos + 1, ['}', ...$stack]),=0A=
>         '<' =3D> parse($line, $pos + 1, ['>', ...$stack]),=0A=
>         '(' =3D> parse($line, $pos + 1, [')', ...$stack]),=0A=
>         '[' =3D> parse($line, $pos + 1, [']', ...$stack]),=0A=
>         '}', '>', ')', ']' =3D> $next =3D=3D=3D $head ? parse($line, $pos=
 + 1, array_slice($stack, 1)) : $next,=0A=
>         null =3D> count($stack) ? Result::Incomplete : Result::OK,=0A=
>     };=0A=
> }=0A=
>=0A=
> The interesting part is the ['<', ...$stack], to pass on a modified versi=
on of an array-as-stack.  That's of course annoyingly slow with arrays righ=
t now, and a Deque would be better, but only if it could be "modified and p=
assed" like that.  If not, it would be incompatible with single-expression =
usages (match statements, short lambdas, etc.)=0A=
>=0A=
> Returning $this would resolve that, I think.  (Making it return a new, im=
mutable copy of the Deque would be even nicer, but I realize that's probabl=
y not an argument I'm going to win at this point on this RFC.)=0A=
=0A=
Technically, you still can have single-expression usages in readable/unread=
able ways=0A=
=0A=
- `[$deque->shift('value'), $deque][1]`, or=0A=
- `($deque->shift('value') ?: $deque)`, or=0A=
- `my_userland_helper_shift_and_return($deque, 'value')`=0A=
=0A=
My personal preference is against making this fluent.=0A=
I'd rather expose an efficient datastructure that's consistent with the res=
t of PHP's functionality to the extent possible,=0A=
which userland can use to write their own fluent/non-fluent classes.=0A=
There's drawbacks to returning `$this`, including:=0A=
=0A=
1. Inconsistency with existing APIs making remembering what does what harde=
r. Barely anything in php that I remember returns $this.=0A=
=0A=
   https://www.php.net/manual/en/arrayobject.append.php returns void.=0A=
=0A=
   https://www.php.net/manual/en/function.array-push returns an int.=0A=
2. Inconsistency with possible new datastructures/methods=0A=
=0A=
   If a `Map`/`Set` function were to be added, then methods for add/remove =
would return booleans (or the old value), not $this=0A=
=0A=
3. Slight additional performance overhead for functionality I assume will b=
e used relatively infrequently=0A=
=0A=
   (php has to increment reference counts and opcache can't eliminate the o=
pcode to decrease reference counts and possibly free the return value of `$=
deque->shift()` with the return type info being an object)=0A=
4.  Returning $this makes code easier to write at some cost to readability =
- Developers new to php or using `Collections\Deque` for the first time wou=
ld not immediately know what the code they're reading is doing.=0A=
   (less of a problem with a good IDE, typechecker, and a typed codebase, b=
ut this isn't universal)=0A=
   Having it return void, `return $deque->push()` would be less common and =
this would force the meaning to be clear.=0A=
=0A=
   Developers might have several guesses/assumptions based on their experie=
nce with other methods in php/elsewhere=0A=
=0A=
   - It returns the new count (JavaScript Array.push, array_push)=0A=
   - It returns $this (Ruby)=0A=
   - It returns a lazy copy, like you'd wanted, not modifying the original=
=0A=
   - It's returning void and the code in question is shorthand for `return =
null`.=0A=
     (Python, C++ https://www.cplusplus.com/reference/vector/vector/push_ba=
ck/ , offsetSet and spl push()/shift() methods)=0A=
=0A=
> Also, typo:=0A=
>=0A=
> "By introducing a data structure (Deque) that's even faster and more memo=
ry usage than an array for use as a double-ended queue, even more applicati=
ons would benefit from it. "=0A=
>=0A=
> I think you mean "less memory usage", or possibly "more memory efficient"=
, or something like that.=0A=
=0A=
Thanks, I've fixed that.=0A=
=0A=
Thanks,=0A=
Tyson=0A=