rfc:short_closures
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rfc:short_closures [2015/05/01 18:39] – bwoebi | rfc:short_closures [2017/09/22 13:28] (current) – external edit 127.0.0.1 | ||
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* Date: 2015-05-01 | * Date: 2015-05-01 | ||
* Author: Bob Weinand, bobwei9@hotmail.com | * Author: Bob Weinand, bobwei9@hotmail.com | ||
- | * Status: | + | * Status: |
* First Published at: http:// | * First Published at: http:// | ||
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</ | </ | ||
- | Anonymous functions defined in this way will automatically use() all of the compiled variables in the local scope. See the ' | + | Anonymous functions defined in this way will automatically |
==== Syntax ==== | ==== Syntax ==== | ||
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Omitting the parentheses when the function has multiple parameters will result in a parse error: | Omitting the parentheses when the function has multiple parameters will result in a parse error: | ||
<code php> | <code php> | ||
- | $x, $y ~> {$x + y} // Unexpected ',' | + | $x, $y ~> {$x + $y} // Unexpected ',' |
+ | ($x, $y) ~> $x + $y // correct | ||
</ | </ | ||
Using the return keyword when braces have been omitted, will similarly give a parse error: | Using the return keyword when braces have been omitted, will similarly give a parse error: | ||
<code php> | <code php> | ||
- | ($x, $y) ~> return $x + y; // Unexpected T_RETURN | + | ($x, $y) ~> return $x + $y; // Unexpected T_RETURN |
+ | ($x, $y) ~> { return $x + $y; } // correct | ||
</ | </ | ||
- | Concrete syntax is (~> is right associative with lowest possible | + | In case of no parameters, an empty parenthesis pair is needed. |
+ | <code php> | ||
+ | ~> 2 * 3; // Unexpected T_TILDED_ARROW | ||
+ | () ~> 2 * 3; // correct, will return 6 when called | ||
+ | </ | ||
+ | |||
+ | Concrete syntax is (~> is right associative with lowest possible | ||
< | < | ||
( parameter_list ) ~> expression | ( parameter_list ) ~> expression | ||
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When a bare expression is used as second parameter, its result will be the return value of the Closure. | When a bare expression is used as second parameter, its result will be the return value of the Closure. | ||
+ | |||
+ | Also, parameter_list does //not// include default values nor type hints. See also the 'Type Hints and Return Types' section at the bottom. | ||
+ | |||
+ | // | ||
+ | This RFC stance is that chained short Closures followed by a full Closure would look quite weird: '' | ||
+ | |||
+ | // | ||
+ | While it might appear not consistent, with any other number of parameters, a lot of languages having extra short Closures allow this. Also, Closures with just one parameter are relatively common, so this RFC author thinks it is worth supporting that. | ||
==== Variable binding ==== | ==== Variable binding ==== | ||
- | The position of this RFC is that the shorthand syntax is to allow anonymous functions to be used as easily as possible. Therefore, rather than requiring individual variables be bound to the closure through the '' | + | The position of this RFC is that the shorthand syntax is to allow anonymous functions to be used as easily as possible. Therefore, rather than requiring individual variables be bound to the closure through the '' |
- | For example: | + | The variable binding is always **by value**. There are no implicit references. If these are needed, the current syntax with '' |
+ | For example: | ||
<code php> | <code php> | ||
$a = 1; | $a = 1; | ||
Line 98: | Line 115: | ||
==== Array sort with user function ==== | ==== Array sort with user function ==== | ||
- | Sort '' | + | Sort '' |
Current syntax: | Current syntax: | ||
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usort($array, | usort($array, | ||
function($a, | function($a, | ||
- | return | + | return $a->val <=> $b-> |
} | } | ||
); | ); | ||
Line 111: | Line 128: | ||
New syntax: | New syntax: | ||
<code php> | <code php> | ||
- | usort($array, | + | usort($array, |
</ | </ | ||
Line 119: | Line 136: | ||
function sumEventScores($events, | function sumEventScores($events, | ||
$types = array_map( | $types = array_map( | ||
- | function ($event) { | + | function($event) { |
return $event[' | return $event[' | ||
}, | }, | ||
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return array_reduce( | return array_reduce( | ||
$types, | $types, | ||
- | function ($sum, $type) use ($scores) { | + | function($sum, |
return $sum + $scores[$type]; | return $sum + $scores[$type]; | ||
} | } | ||
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sumEventScores($events, | sumEventScores($events, | ||
+ | </ | ||
+ | |||
+ | ==== Lazy evaluation ==== | ||
+ | It may be necessary to have code only evaluated under specific conditions, like debugging code: | ||
+ | <code php> | ||
+ | function runDebug(callable $func) { | ||
+ | /* only run under debug situations, but don't let it interrupt program flow, just log it */ | ||
+ | if (DEBUG) { | ||
+ | try { | ||
+ | $func(); | ||
+ | } catch (Exception $e) { /*... */ } | ||
+ | } | ||
+ | } | ||
+ | |||
+ | $myFile = "/ | ||
+ | |||
+ | /* Old code */ | ||
+ | runDebug(function() use ($myFile) { /* yeah, we have to use use ($myFile) here, which isn't really helpful in this context */ | ||
+ | if (!file_exists($myFile)) { | ||
+ | throw new Exception(" | ||
+ | } | ||
+ | }); | ||
+ | |||
+ | /* New code */ | ||
+ | runDebug(() ~> { | ||
+ | if (!file_exists($myFile)) { | ||
+ | throw new Exception(" | ||
+ | } | ||
+ | }); | ||
+ | |||
+ | /* still continue here, unlike an assert which would unwind the stack frame here ... */ | ||
</ | </ | ||
==== Partial application ==== | ==== Partial application ==== | ||
- | The short hand syntax makes it easier to write functional code like a reducer by using the ability of shorthand anonymous functions to be chained together easily. | + | The shorthand |
Current syntax: | Current syntax: | ||
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function reduce(callable $fn) { | function reduce(callable $fn) { | ||
return function($initial) use ($fn) { | return function($initial) use ($fn) { | ||
- | return function ($input) use ($fn, $initial) { | + | return function($input) use ($fn, $initial) { |
$accumulator = $initial; | $accumulator = $initial; | ||
foreach ($input as $value) { | foreach ($input as $value) { | ||
Line 213: | Line 261: | ||
return [$x => $x * 2]; | return [$x => $x * 2]; | ||
</ | </ | ||
+ | |||
+ | Additionally, | ||
+ | |||
+ | Also, Hack has some possibilities of typing here, which do not work with PHP, due to technical reasons. Regarding forward compatibility, | ||
===== Backward Incompatible Changes ===== | ===== Backward Incompatible Changes ===== | ||
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private $bar: | private $bar: | ||
- | getBar ~> $this-> | + | getBar() ~> $this-> |
setBar($bar) ~> $this-> | setBar($bar) ~> $this-> | ||
} | } | ||
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As an alternative, | As an alternative, | ||
- | ===== Proposed Voting Choices | + | ===== Vote ===== |
This RFC is a language change and as such needs a 2/3 majority. | This RFC is a language change and as such needs a 2/3 majority. | ||
- | It will be a simple yes/no vote. | + | Voting opened September 22th, 2015 and will remain open until October 2nd, 2015. |
+ | |||
+ | <doodle title=" | ||
+ | * Yes | ||
+ | * No | ||
+ | </ | ||
===== Patch ===== | ===== Patch ===== | ||
Pull request is at https:// | Pull request is at https:// |
rfc/short_closures.1430505582.txt.gz · Last modified: 2017/09/22 13:28 (external edit)