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Date: Mon, 20 Jan 2014 08:31:17 +0100
Message-ID: <CAJ26g5T9R8U4dJrmr1E-XZCe=RH65QQCEt7F5dQ1MfsR+LbSZQ@mail.gmail.com>
To: Larry Garfield <larry@garfieldtech.com>
Cc: internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001a11c13010a0627404f061e0f4
Subject: Re: [PHP-DEV] Introducing "Array Of" RFC
From: bof@bof.de (Patrick Schaaf)

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Content-Type: text/plain; charset=ISO-8859-1

Regarding the N*M checking complexity, couldn't a little bit of memory
alleviate the problem?

For each array, have a "member type" pointer, initially NULL.

When the member type needs to be checked for the first time, and that
"member type" pointer is not already set, do an O(N) scan of the arrray,
testing compatibility of all members against the hinted type. Error on
mismatch, but when all members match, remember the type behind the "member
type" pointer.

When the member type needs to be checked and the "member type" pointer _is_
set, just compare it to the hinted type O(1).

There must be some overhead when elements are added to an array. Either
"when member type is set, forget it", or even "when member type is already
set, check compatiility of the newly added element with the member type,
and then remove member type on mismatch or keep it on match".

Finally when arrays are copied, and "member type" is already set, copy it
along with the array, Optionally some of the array functions like
array_merge might be made aware of the scheme, too.

BTW, I'm undecided regarding the need for the overall feature, from my
rather limited personal coding practise it seems to me that whenever I am
interested in member type checking I'm already looping over the array and
can easily add up-front instanceof checks to the loops with suitable
explicit error-out. Which I generally prefer over automatic errors,
especially fatal ones, because _I_ control the error case behaviour.

But I think _if_ such a scheme were added, the implementation described
above would solve the O(N*M) problem with acceptable overall cost.

best regards
  Patrick

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