> arrays-that-are-arrays-sometimes-but-maps-other-times

god, the time i spent going paranoid debugging a stray "undefined array index 0" just to find out

  array_filter(
    is_uppercase,
    ['a', 'B', 'c', 'D']
  )

returns

  [1 => 'B', 3 => 'D']

and not

  ['B', 'D']

like every other `filter(...)` i've used...

EDIT to be fair, i see the rationale – having the index of the filtered element is useful sometimes, and requires some contortions with the usual impl of filter. it's quite neat, because you get both the index and the elements! but it's just... surprising as the default, and PHP's conflation of maps and lists obscures it – all the docs say is "array keys are preserved", which makes sense in retrospect, but doesn't really jump out for something with this much impact

This is exactly the sort of thing that bites. It totally breaks your functional pipelines: now you have to thread everything through `array_values`. Ew ew ew. No thank you.

On the other hand, having learned PHP inside-out as my first language, this is perfectly natural to me, and I miss the flexibility of PHP arrays in other languages :)

Never heard anyone complain about scoping or closure issues with PHP. I'd be interested to hear more if you recall.

I don’t believe there are maps in PHP - just plain arrays which to be honest are pretty simple to use. Unlike say JavaScript where arrays are always numerically indexed, PHP can use any value as an index.

JavaScript, by contrast, doesn't have arrays - it just has objects, which can have numerical keys.

  a = []
  a.foo = 'bar' // works!

  b = {}
  b[0] = 42 // also works!

I happen to think these designs are both INSANE, but even if you like them, PHP has no advantage here.

I’m pretty sure this is wrong. JS objects and arrays are different. The former will only yield elements from the array itself when iterated on, and has a consistent iteration order, while the later does not.

That's because arrays happen to override the special [Symbol.iterator] method:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

Arrays are objects of class Array which have special literals, override the toString() method, and update the non-enumerable "length" property on certain operations.

Try calling Object.keys([1, 2, 3]), or even better try Object.getOwnPropertyNames([1, 2, 3])

Order is consistent in both

https://www.stefanjudis.com/today-i-learned/property-order-i...

JS arrays are array-like objects. That's the official line anyway.

so isn't it like PHP, which doesn't have lists, only maps with integer keys?

With the exception that unlike (I think?) PHP, JS also uses maps (w hich can only have string keys [1]) to implement objects and classes. Hence their being called objects, not maps.

[1] So how do arrays have numerical keys? Well... actually they don't. I was trying to make JS look better than it is in my original comment. Actually, array keys are stringified versions of numbers, and values are automatically cast to string when you put them in indexing braces.

  Object.keys([1, 2])
  --> ["0",  "1"]

As you can imagine, this leads to gotchas when you assume that a JS object can have, say, a date as a key

  b = {}; b[new Date()] = 10;
  Object.keys(b)
  --> [
    "Sat Nov 09 2019 23:15:58 GMT-0800 (Pacific Standard Time)"
  ]

i think that's just a matter of naming – afaik PHP "arrays" are what you'd call a map/dict/hash in other languages

I believe it is just a naming issue. Not even sure that PHP devs have agreed on how to name the type. Internally, PHP calls them both arrays and hash tables if I understand correctly.

In Zend/zend_types.h[1] of PHP source:

    typedef struct _zend_array zend_array;
    typedef struct _zend_array HashTable;
    struct _zend_array {
        ...
    };

That being said AFAICT, HashTable and zend_array are used interchangeably throughout the source. I am not a C programmer, but I did write a couple of PHP extensions and that was my general understanding. Perhaps it is a compatibility issue or just used to abstract types differently in various areas of the C API.

Check out [2] for a deeper understanding of how arrays are handled internally in PHP.

[1]: https://github.com/php/php-src/blob/php-7.3.11/Zend/zend_typ...

[2]: https://nikic.github.io/2014/12/22/PHPs-new-hashtable-implem...

rtm ?

"An array in PHP is actually an ordered map."

https://www.php.net/manual/en/language.types.array.php