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To: "Stas Malyshev" <smalyshev@sugarcrm.com>
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Date: Tue, 29 May 2012 10:05:06 +0200
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Subject: Re: [PHP-DEV] [VOTE] array_part()
From: glopes@nebm.ist.utl.pt ("Gustavo Lopes")

On Tue, 29 May 2012 02:28:05 +0200, Stas Malyshev <smalyshev@sugarcrm.com>  
wrote:

> This looks very complicated. It might be that some use cases require
> this level of complexity, but I can't remember a case where I would need
> it. That alone does not disqualify the proposal, but I personally very
> much like having something like array_column() rather than whole array
> slicing engine with it's own declarative language inside. The engine
> might be fine, but I imagine many users would want just something like
> array_column() - so at least it'd be nice to have both.

1)
Independently for whether we want array_column this function does things  
that no other function built-in currently does and some that no userland  
function can even do:

* Extract slices without side effects (array_slice() has side effects).
* Extract slices based on keys on time proportional to the size of the  
slice and not to the size of the array.
* Pick an arbitrary number of elements from an array in any permutation  
and traversing the array, in worst case -- if we request an element in the  
middle --, only once.

2)
A lot of people seem to think this is too complicated. I think that  
objection comes from several places:

* People focusing on the most complex usages of the function. The test  
cases have to cover complex usages in order to exercise the implementation  
correctly, but that doesn't mean the majority of use cases will be that  
complex.
* The syntax for contiguous slices is verbose (e.g. ['start'=>1, 'end'=>3]  
instead of [1:3] or [1..3] like in other languages).
* Specifying we want all the elements in a level could be simpler (e.g.  
using null instead of ['start'=>0] or ['start'=>null]). See above.
* The description of the function aims to be precise and is therefore  
verbose. This was probably a strategic miscalculation on my part.

Let me exemplify how this function may make things simpler. Right now,  
let's suppose you want to drop the first element on each level. Let's say  
you have this array:

$arr =
[
   ['col1',  'col2', 'col3'],
   ['line1', 0,      1     ],
   ['line2', 1,      0     ],
]

To drop the headers, you'd now have to do:

array_slice(array_map(function($a) { return array_slice($a,1); }, $arr),  
1);

With array_part, you can do:

array_part($arr, [ ['start'=>1], ['start'=>1] ]);

or in this case:

array_part($arr, [ [1, 2], [1, 2] ]);
-- 
Gustavo Lopes