rfc:array_key_first_last_index

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rfc:array_key_first_last_index [2015/12/07 17:58]
jbafford
rfc:array_key_first_last_index [2017/09/22 13:28] (current)
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 ====== PHP RFC: array_key_(first|last|index) ====== ====== PHP RFC: array_key_(first|last|index) ======
-  * Version: 1.0 +  * Version: 1.0.1 
-  * Date: 2015-12-05+  * Date: 2016-01-01
   * Author: John Bafford   * Author: John Bafford
-  * Status: ​Draft+  * Status: ​Under Discussion
   * First Published at: http://​wiki.php.net/​rfc/​array_key_first_last_index   * First Published at: http://​wiki.php.net/​rfc/​array_key_first_last_index
  
  
 ===== Introduction ===== ===== Introduction =====
-This RFC and its accompanying patch add the following functions:+Sometimes, it is necessary to retrieve the first or last key of an array, but there is no convenient means of doing so currently provided by the language without modifying the source array or resorting to odd-to-read code. This RFC and its accompanying patch add the following functions ​to assist with that task:
  
   * $key = array_key_first($array [, &​$value])   * $key = array_key_first($array [, &​$value])
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 ===== Proposal ===== ===== Proposal =====
 +Arrays in php are ordered maps, but there is no convenient way to get the first or last key of an array (a common function in some use cases), or even an arbitrary key by index (a fairly rare need).
 +
 array_key_first() returns the first key in an array. array_key_first() returns the first key in an array.
  
 array_key_last() returns the last key in an array. array_key_last() returns the last key in an array.
  
-array_key_index() returns the key at a specified index (using a substr-like offset; ​positive ​starts from the beginning of the array; negative from the end).+array_key_index() returns the key at a specified index (using a substr-like offset; ​greater-than or equal to zero starts from the beginning of the array; negative from the end). 
 + 
 +<code php> 
 +$arr ['​a'​ => 1, '​b'​ => 2, '​c'​ => 3, '​d'​ => 4]; 
 + 
 +$key = array_key_first($arr);​ //$key === '​a'​ 
 + 
 +$key = array_key_last($arr,​ $val); //$key === '​d',​ $val === 4 
 + 
 +$key = array_key_index($arr,​ 1); //$key === '​b'​ 
 +$key = array_key_index($arr,​ -2); //$key === '​c'​ 
 +$key = array_key_index($arr,​ 5, $val); //$key === NULL, $val is unchanged 
 + 
 + 
 +// Also works for numeric arrays 
 +$numeric = [1 => 1, 5 => 2, 2 => 3]; 
 +$key = array_key_index($numeric,​ 0); //$key === 1 
 +$key = array_key_index($numeric,​ 1); //$key === 5 
 +$key = array_key_index($numeric,​ 2); //$key === 2 
 +</​code>​ 
  
 All three functions return the requested array key, or null if the requested array key is not found (an empty array, or an out-of-bounds index in the case of array_key_index). For convenience,​ each function also takes an optional $value parameter that, if provided and the specified index is found, will be set to contain the value at the specified index. All three functions return the requested array key, or null if the requested array key is not found (an empty array, or an out-of-bounds index in the case of array_key_index). For convenience,​ each function also takes an optional $value parameter that, if provided and the specified index is found, will be set to contain the value at the specified index.
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       * foreach($arr as $key => $value); //Iterate over the entire array, doing nothing, just for the side-effect of $key still contains the last array key beyond the end of the loop.//       * foreach($arr as $key => $value); //Iterate over the entire array, doing nothing, just for the side-effect of $key still contains the last array key beyond the end of the loop.//
  
-  * reset($arr);​ $key = current($arr);+  * reset($arr);​ $key = key($arr);​ 
 +  * end($arr); $key = key($arr);
     * This modifies the array (resets the array pointer).     * This modifies the array (resets the array pointer).
-    * There is no simple way to get either the last key or an indexed key via this method. 
  
 +With the reference implementation provided in the patch referenced below, array_key_first() and array_key_last() directly retrieve the array key from the underlying hash (by setting a local hash pointer to the start/end of the array and retrieving the key for that index). By necessity, array_key_index() iterates through the keys, but does so in C code, rather than in PHP code. array_key_first() and array_key_last() are implemented in terms of array_key_index();​ array_key_index() exists a a consequence and extension of generalizing the common code between array_key_first() and array_key_last().
  
-With the reference implementation provided below, ​array_key_first() and array_key_last() ​directly retrieve ​the array key from the underlying hash (by setting ​local hash pointer to the start/end of the array and retrieving the key for that index). By necessity, ​array_key_index() ​iterates through the keys, but does so in C coderather than in PHP code.+array_key_first() and array_key_last() ​have O(1) time complexity. array_key_index() (when not retrieving ​the first or last key) has O(N) time complexity. array_key_index() is intended when only one key or value from an array is needed; if repeated calls to array_key_index() are needed for particular ​array, it would likely be more performant to just use array_keys(instead(Iterating all keys of an array using array_key_index() ​would be O(N^2).) As such, it's included for sake of completeness, but would likely ​in practice see limited use. 
 + 
 +===== Patches and Tests ===== 
 +The GitHub Pull request for this change is here: https://​github.com/​php/​php-src/​pull/​347 
 + 
 +This is a full and working implementationand if accepted, could be merged as-is. The PR includes tests covering all new functionality.
  
 ===== Backward Incompatible Changes ===== ===== Backward Incompatible Changes =====
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 ===== Open Issues ===== ===== Open Issues =====
-None noted at this time.+* Whether or not to include the corresponding array value as an optional-return-by-reference parameter.
  
 ===== Proposed Voting Choices ===== ===== Proposed Voting Choices =====
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 This RFC does not add new syntax, so a 50%+1 majority is required to pass. This RFC does not add new syntax, so a 50%+1 majority is required to pass.
- 
-===== Patches and Tests ===== 
-The GitHub Pull request for this change is here: https://​github.com/​php/​php-src/​pull/​347 
- 
-This is a full and working implementation,​ and if accepted, could be merged as-is. 
  
 ===== Implementation ===== ===== Implementation =====
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   - a link to the git commit(s)   - a link to the git commit(s)
   - a link to the PHP manual entry for the feature   - a link to the PHP manual entry for the feature
- 
rfc/array_key_first_last_index.1449511125.txt.gz · Last modified: 2017/09/22 13:28 (external edit)