PHP: rfc:alpanumeric_decrement

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====== PHP RFC: Alphanumeric Decrement ======
  * Version: 1.0
  * Date: 2013-12-16
  * Author: Andrea Faulds <ajf@ajf.me>
  * Status: Declined
  * First Published at: http://wiki.php.net/rfc/alphanumeric_decrement

===== Introduction =====

This will add support for decrementing alphanumeric strings ("ab", for example) to complement the existing incrementing behaviour.

===== Proposal =====

At present, incrementing alphanumeric strings is supported. For example:

  $x = "z";
  $x++;
  // $x is now "aa"

However, decrementing alphanumeric strings is not:

  $x = "z";
  $x--;
  // $x is still "z"

Under this proposal, alphanumeric strings would be decrementable:

  $x = "z";
  $x--;
  // $x is now "y"

It would also handle the edge case of decrementing from "a", choosing to result in 0 (this may be subject to change):

  $x = "a";
  $x--;
  // $x is now 0

The patch at present additionally changes how empty strings are incremented. At present, it works as follows:

  $x = "";
  $x++;
  // $x is now "1" (string)
  $x = "";
  $x--;
  // $x is now -1 (int)

With this patch, it is now consistent:

  $x = "";
  $x--;
  // $x is now "-1" (string)

===== Backward Incompatible Changes =====

This might arguably be a BC break, as now decrementing for these strings would work, while existing code might assume that doesn't work. I doubt there is any code relying on that though, especially since "a"++ is a relatively obscure feature.

===== Proposed PHP Version(s) =====

Next PHP 5.x. Failing that, next PHP x.

===== SAPIs Impacted =====

None.

===== Impact to Existing Extensions =====

None.

===== New Constants =====

None.

===== php.ini Defaults =====

None.

===== Open Issues =====

How should decrementing "a" be handled? The patch and behaviour as proposed decrement to 0, however possibly not decrementing and emitting a warning might make more sense.

===== Unaffected PHP Functionality =====

Does not affect $x += 1 and $x -= 1, nor $x = $x + 1 and $x = $x - 1, as both of these do not support alphanumeric increment at present.

===== Future Scope =====

In future, alphanumeric increment being supported $x += 1 and $x = $x + 1 might be desirable, but that is not within the scope of this RFC.

===== Vote =====

Merge into PHP 5.6? (Will assume this requires 2/3 majority, due to new language feature)

Voting started 2014-01-21 and ended 2014-01-28.

<doodle title="Alphanumeric Decrement" auth="ajf" voteType="single" closed="true">
   * Yes
   * No
</doodle>

===== Patches and Tests =====

https://github.com/php/php-src/pull/546

Considered final patch, unless bugs are found.

===== Implementation =====

Not merged in at present.

===== References =====

Mailing list discussion: http://marc.info/?l=php-internals&m=138687859827708&w=1

===== Rejected Features =====

None as yet?
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