PHP: rfc:clamp

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====== PHP RFC: clamp ======
  * Version: 1
  * Date: 2021-06-23
  * Author: Kim Hallberg, hallbergkim@gmail.com
  * Status: Withdrawn
  * Proposed Version: PHP 8.2
  * First Published at: http://wiki.php.net/rfc/clamp

===== Introduction =====
''clamp'' checks if a ''int|float'' value is within a certain bound. If the value is in range it returns the value, if the value is not in range it returns the nearest bound.

Current userland implementations are handled in several ways, some of which use [[https://www.php.net/manual/en/function.min.php|min]] and [[https://www.php.net/manual/en/function.max.php|max]] to check the bound, which is costly and slow when called often. Because userland implementations are for the most part not cost-effective when called multiple times, a language implementation is desired.

===== Proposal =====

This RFC proposes a new function: ''clamp''

<code php>
clamp ( int|float $num, int|float $min, int|float $max ) : int|float
</code>

''clamp'' takes three arguments, a ''$num'', ''$min'' and ''$max'', checks if ''$num'' is within the bounds of ''$min'' and ''$max'', if in range, returns the value of ''$num'', otherwise, returns the nearest bound value, i.e. if ''$num > $max'' return ''$max'', if ''$num < $min'' return ''$min''.

If ''$min'' value is greater than ''$max'' value, a ''ValueError'' will be thrown, since that constitute an invalid bound.

The proposed function as code:

<code php>
clamp(num: 1, min: 0, max: 3); // 1   in range
clamp(num: 1, min: 2, max: 5); // 2   < bound
clamp(num: 4, min: 1, max: 3); // 3   > bound

clamp(num: 0, min: 2, max: 1); // clamp(): Argument #2 ($min) cannot be greater than Argument #3 ($max)
</code>

Handling NAN; passing NAN to either of the range values will throw above ''ValueError'' since passing NAN will invalidate the range.

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

No backwards incompatible changes with PHP itself.

''clamp'' will no longer be available as a function name, could break potential userland implementations. 

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

  * next PHP 8.x

===== RFC Impact =====

  * **To SAPIs:** Function will be added to all PHP enviroments.
  * **To Existing Extensions:** None
  * **To Opcache:** None.
  * **New Contants:** No new constants introduced.
  * **php.ini defaults:** No changes to php.ini introduced.

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

1) Handling of NAN values, as mentioned [[https://externals.io/message/115076#115085|#115085]] and [[https://externals.io/message/115076#115167|#115167]].

===== Proposed Voting Choices =====

The vote will require 2/3 majority.

===== Implementation =====

RFC implementation can be found in the following pull request: [[https://github.com/php/php-src/issues/7191]].

===== References =====

  * Implementation of similar methods/functions in other languages:
      * [[https://en.cppreference.com/w/cpp/algorithm/clamp]]
      * [[https://www.rdocumentation.org/packages/raster/versions/3.4-10/topics/clamp]]
      * [[https://developer.mozilla.org/en-US/docs/Web/CSS/clamp()]]
  * Implementation PR: [[https://github.com/php/php-src/issues/7191]]
  * Discussion on the php.internals mailing list: [[https://externals.io/message/115050]]
  * Announcement thread: [[https://externals.io/message/115076]]

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

No rejected features currently.
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