PHP: rfc:short-match

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====== PHP RFC: Short match ======
  * Version: 1.0
  * Date: 2020-12-13
  * Author: Larry Garfield (larry@garfieldtech.com)
  * Status: Inactive
  * First Published at: http://wiki.php.net/rfc/short-match


===== Introduction =====

The ''match()'' expression, introduced in PHP 8.0, matches one value against a series of others.  For more complex cases, it's possible to provide a value of boolean ''true'' as the value to match against, allowing each branch to be arbitrarily complex as long as it results in a boolean.  This RFC allows that case to be used as a default; It makes the value to match against optional, and defaults it to boolean ''true'' if not specified.

This functionality was included in the original [[rfc:match_expression|Match expression v1]] RFC.  It was removed from the second [[rfc:match_expression_v2|Match expression v2]] RFC for simplicity.  However, the poll from the first RFC suggested this was a desired feature, so this RFC brings it back.

===== Proposal =====

This RFC would make only one change.  In a ''match()'' expression, if the match subject were not provided, it would default to boolean ''true''.

That is, this PHP 8.0 syntax:

<code php>
$a = 3;

print match (true) {
  $a < 2 => 'small',
  $a == 3 => 'medium',
  default => 'large',
};
</code>

could, with this RFC, be shortened to:

<code php>
$a = 3;

print match {
  $a < 2 => 'small',
  $a == 3 => 'medium',
  default => 'large',
};
</code>

A prime use case for such match statements is for basic pattern matching within a function:

<code php>
function getNumberKind(int $num) {
  return match {
    $num > 0 => NumberKind::POSITIVE,
    $num == 0 => NumberKind::ZERO,
    $num < 0 => NumberKind::NEGATIVE,
  };
}
</code>

That would be even more compact if combined with the also-proposed [[rfc:short-functions|Short Functions]] RFC.  Or, if used with a short-lambda today:

<code php>
$getNumber = fn(int $num) => match {
    $num < 0 => NumberKind::NEGATIVE,
    $num == 0 => NumberKind::ZERO,
    $num > 0 => NumberKind::POSITIVE,
};
</code>

The net result is to simplify both the writing and reading of "functions as expressions" rather than "functions as subroutines."

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

None

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

8.1


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

Accept this RFC as proposed. 2/3 required for passage.

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

[[https://github.com/php/php-src/pull/6511|PR available here]]

===== Implementation =====


===== References =====

  * [[rfc:match_expression|PHP RFC: Match expression]]
  * [[rfc:match_expression_v2|PHP RFC: Match expression v2]]
  * [[rfc:short-functions|PHP RFC: Short Functions]]
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