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Comment by noduerme | Hacker News Reader

Agree, the ... syntax feels confusing when each fn($x) in the example uses $x as the name of its argument.

My initial instinct would be to write like this:

`$result = $arr

    |> fn($arr) => array_column($arr, 'tags') // Gets an array of arrays

    |> fn($cols) => array_merge(...$cols)`

Which makes me wonder how this handles scope. I'd imagine the interior of some chained function can't reference the input $arr, right? Does it allow pass by reference?

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You can do

     function ($parameter) use ($data) { ... }

to capture stuff from the local environment.

Edit: And you can pass by reference:

   > $stuff = [1]
   = [
       1,
     ]

   > $fn = function ($par) use (&$stuff) { $stuff[] = $par; }
   = Closure($par) {#3980 …2}

   > $fn(2)
   = null

   > $stuff
   = [
       1,
       2,
     ]

Never done it in practice, though, not sure if there are any footguns besides the obvious hazards in remote mutation.

idk if it counts as an obvious hazard, but being able to modify the original input by reference within a chain of piped functions definitely makes it a lot harder to reason about what that sequence might be doing. Particularly since we assume that arrays are passed by reference anyway unless the function you're calling is making a shallow copy of their elements.

My feeling is that this makes the code less legible. I'd rather write 5 lines of code that mutate an object or return a copy than do a pipe this way. I'm sort of not excited to start running into examples of this in the wild.

You can write it this way. The parameter name is arbitrary. And no, to my knowledge you can't access the var from the previous scope

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