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Date: Sun, 17 Nov 2019 19:27:41 +0000
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Subject: Re: [PHP-DEV] Concept: "arrayable" pseudo type and \Arrayable
 interface
From: rowan.collins@gmail.com (Rowan Tommins)

[Note: I've included the full text of the previous message as it wasn't 
sent to the list.]

On 17/11/2019 18:35, Aimeos | Norbert Sendetzky wrote:
>> It feels like there are two alternative suggestions here. Not only do
>> they use the same keyword to mean different things, but "convertible to
>> array", and "usable as array" seem like distinct concepts to me.
> The name of the interface isn't perfect because it may be too close to
> the type hint and therefore misleading. Suggestions for a better name
> are always welcome.
>
> The concept contains three parts:
> - arrayable type hint: Use objects and arrays alike
> - \Arrayable interface: To enable implementing objects that are "arrayable"
> - __toArray(): To convert objects to arrays


Like I say, the name is part of it, but the purposes also overlap the 
way you describe them. It makes more sense to me to have two separate 
features for two separate use cases:

- If I just want to know that the object I've received can be iterated, 
counted, and accessed using square brackets, then I need either a 
special type hint or a new interface, but not both.
- On the other hand, if I just want to know I can call toArray or 
__toArray on an object, I don't care whether it implements Iterator, 
Countable, etc as well.



>> For the "convertible to array" case, I think __toArray, or an interface
>> specifying just that one method, would make more sense than combining it
>> with the existing interfaces. I'm sceptical of that concept, though,
>> because most objects could be converted to many different arrays in
>> different circumstances, each of which should be given a different and
>> descriptive name.
> Can you give some examples for different conversions?


Well, pretty much any method that returns array *could* be called "to 
array", but not many would be good candidates for such a generic name. 
You might return an array structure to be incorporated into a JSON 
response, or to be passed to a template renderer, or to map to database 
columns, etc.

The only case I can think of where a generic "toArray" method would make 
sense is if you're creating a general-purpose "collection" or "list" 
object, in which case you're probably better off directly implementing 
methods like map and sort, rather than encouraging users to convert it 
back to a plain array. It doesn't seem like a common enough use case to 
need a new language feature, when it's simple enough to write 
"$foo->toArray()" without anything new.


> The possibility to pass arrayable objects to the array_* methods should
> be out of scope for the moment and is better discussed later to keep the
> pieces small, I think. You are totally right, there may be some
> unexpected behavior when doing that.


The reason I mentioned it is that without it the new type hint or 
interface seems rather limited: I can't imagine many "array" type 
constraints being replaced with "arrayable" if you had to remember not 
to pass the variable to array_map, sort, etc.


Regards,

-- 
Rowan Tommins (né Collins)
[IMSoP]