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Date: Tue, 2 May 2017 12:41:41 +0100
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Subject: Re: [PHP-DEV] Add is_vectorlike($array) function
From: rowan.collins@gmail.com (Rowan Collins)

On 02/05/2017 11:53, Giovanni Giacobbi wrote:
> Wouldn't be better to introduce a new native type "vector"? I know it 
> sounds obnoxious introducing a new basic data type, but I think having 
> a workaround like is_vectorlike() wouldn't completely address the problem.
...
> function do_something_ex(vector $a) {
>   // do something with $a
> }

I can certainly sympathise with the desire to have this built into the 
type hint, but I think it leads to awkward questions about what kind of 
"type" this would be.

If it was a "real" type, that would imply users could explicitly 
construct it in some way, presumably with a new keyword. Indeed, in 
strict_types mode, they would presumably be *obliged* to do so, or cast 
their values, leading to noise like do_something_ex( (vector)$some_array );

It would be better in that case to have generics and a built-in List<T> 
type, so we could type hint for List<int> without the performance hit of 
checking the member types on every function call.


If, on the other hand, it was a pseudo-type only available in type 
hints, then it raises the question of why this particular check gets a 
keyword but others don't. For instance, positiveInt, nonNegativeInt, 
nonEmptyString, finiteFloat, etc, would all be similar in 
implementation: "assert type is X and condition Y is true". If not a 
real type, then "vector" is fundamentally a constrained domain of 
"array" values.


I also wouldn't call is_vectorlike() a workaround, as it serves a 
different use case and would be necessary even if we had a vector type 
hint. You can't choose a code path based on a type hint, since we don't 
have function overloading (which is probably sensible in a dynamic type 
system). We can always add the type hint later, as happened with the 
"callable" type hint.


>   $a = [ "a", "b", "c" ];
>   is_vector($a); // true
>   is_array($a); // true
>   unset($a[1]);
>   is_vector($a); // false
>   is_array($a); // true


Other than the name of the function, this is exactly how the proposed 
function would behave. Note that in this example, "vector" doesn't 
behave like a type, since is_array() returns true, and gettype() would 
still return 'array'.

Regards,

-- 
Rowan Collins
[IMSoP]