rfc:ifsetor

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rfc:ifsetor [2008/06/21 20:36] lsmithrfc:ifsetor [2017/09/22 13:28] (current) – external edit 127.0.0.1
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   * Date: 2008-06-21   * Date: 2008-06-21
   * Author: Lukas Smith <smith@pooteeweet.org>   * Author: Lukas Smith <smith@pooteeweet.org>
-  * Status: Under Discussion+  * Status: Declined
  
-This RFC proposes an operator that efficiently implements (isset($foo) ? $foo : $bar) as ifsetor($foo, $bar).+This RFC proposes an operator that efficiently implements (isset($foo) ? $foo : $bar) as ifsetor($foo, $bar). However this proposal has not been accepted, mainly due to the existance of the userland implementation #2. Of course once a true COALESCE() with any number of parameters could be supported, the situation would be different, since obviously using the "hack" of a pass by reference variable would require hardcoding the number of optional parameters.
  
 ===== Introduction ===== ===== Introduction =====
  
 Frequently PHP developers need to initialize some variable that is passed in via the outside to some value. This leads to repeated code, that is needlessly prone to typos as well as some performance overhead. Frequently PHP developers need to initialize some variable that is passed in via the outside to some value. This leads to repeated code, that is needlessly prone to typos as well as some performance overhead.
- +==== Why do we need ifsetor()? ====
-==== Why do we need RFCs? ====+
  
 Frequently developers need to use the following code constructs: Frequently developers need to use the following code constructs:
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 </code> </code>
  
-Furthermore ifsetor() would support expressions in all but the first parameter, that would only be evaluated if all of the previous parameters were either null or evaluated to null. In the following example the really_expensive_function() should not get called in most cases.+Furthermore ifsetor() would support expressions in the second parameter, that would only be evaluated if all of the previous parameter were either null or evaluated to null. In the following example the really_expensive_function() should not get called in most cases.
  
 <code php> <code php>
 function foo() { return (rand(0, 100) < 100 ? true : null); } function foo() { return (rand(0, 100) < 100 ? true : null); }
-$var = ifsetor($var, foo(), really_expensive_function());+$foo = foo(); 
 +$var = ifsetor($foo, really_expensive_function());
 </code> </code>
  
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 This however is a deviation of the implementation of COALESCE() for example in SQLite, where at least [[http://www.sqlite.org/lang_corefunc.html|2 parameters are required]]. This however is a deviation of the implementation of COALESCE() for example in SQLite, where at least [[http://www.sqlite.org/lang_corefunc.html|2 parameters are required]].
- +==== userland #1 ====
-==== userland alternatives ====+
  
 Another misconception is that the functionality could be implemented in userland. This would prevent several key advantages of ifsetor(). Another misconception is that the functionality could be implemented in userland. This would prevent several key advantages of ifsetor().
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     }     }
 </code> </code>
 +
 +==== userland #2 ====
  
 A more flexible approach would make it possible to handle non arrays as well. The below is a simple implementation [[http://marc.info/?l=php-internals&m=108940007627089&w=2|proposed on the list]]. The use of pass by reference would prevent the notice from being thrown for the first parameter only. It also has some minor [[http://marc.info/?l=php-internals&m=111875921829669&w=2|implications on memory management]], since the below example would create a variable $foo with the value null in the current namespace (unless of course $x would be replaced with $foo in the below example). A more flexible approach would make it possible to handle non arrays as well. The below is a simple implementation [[http://marc.info/?l=php-internals&m=108940007627089&w=2|proposed on the list]]. The use of pass by reference would prevent the notice from being thrown for the first parameter only. It also has some minor [[http://marc.info/?l=php-internals&m=111875921829669&w=2|implications on memory management]], since the below example would create a variable $foo with the value null in the current namespace (unless of course $x would be replaced with $foo in the below example).
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 The obvious problem is that all expressions would always be evaluated, even if their return value will not be used. This brings with it a significant performance overhead and can even lead to bugs if the expression creates side effects that should only occur if the expression was actually used to generate the value for the variable. The obvious problem is that all expressions would always be evaluated, even if their return value will not be used. This brings with it a significant performance overhead and can even lead to bugs if the expression creates side effects that should only occur if the expression was actually used to generate the value for the variable.
 +
 ===== Proposal and Patch ===== ===== Proposal and Patch =====
  
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   - The default value can be omitted in which case NULL will be used.   - The default value can be omitted in which case NULL will be used.
  
-http://marcus-boerger.de/php/ext/ze2/ze2-ifsetor-20040416-2.diff.txt (file no longer exists)+http://php.net/~helly/ze2-ifsetor-20040901.diff.txt
  
 ===== Rejected Features ===== ===== Rejected Features =====
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   * Suggestion to add [[http://marc.info/?l=php-internals&m=113210592810849&w=2|macro]] [[http://marc.info/?l=php-internals&m=116361059402342&w=2|support]] to make it easier to reuse complex userland code pieces to keep the code more readable when handling some of the above aspects in userland   * Suggestion to add [[http://marc.info/?l=php-internals&m=113210592810849&w=2|macro]] [[http://marc.info/?l=php-internals&m=116361059402342&w=2|support]] to make it easier to reuse complex userland code pieces to keep the code more readable when handling some of the above aspects in userland
   * [[http://marc.info/?l=php-internals&m=118946242013246&w=2|Request to add a native function to handle the limited case of a single dimensional array]]    * [[http://marc.info/?l=php-internals&m=118946242013246&w=2|Request to add a native function to handle the limited case of a single dimensional array]] 
 +  * [[http://marc.info/?l=php-internals&m=108955534724882&w=2|Suggestion to fo with the ifsetor() as is]] and later try to find a way to implement a true coalesce() with the name "coalesce()"
rfc/ifsetor.1214080615.txt.gz · Last modified: 2017/09/22 13:28 (external edit)