rfc:partial_function_application

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rfc:partial_function_application [2021/06/02 17:26] – Magic methods work again. crellrfc:partial_function_application [2025/04/03 13:08] (current) – external edit 127.0.0.1
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   * Date: 2020-04-22   * Date: 2020-04-22
   * Author: Paul Crovella, Levi Morrison, Joe Watkins, Larry Garfield   * Author: Paul Crovella, Levi Morrison, Joe Watkins, Larry Garfield
-  * Status: In Discussion+  * Status: Declined
   * First Published at: https://wiki.php.net/rfc/partial_function_application   * First Published at: https://wiki.php.net/rfc/partial_function_application
  
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 // Ex 10 // Ex 10
-$c = stuff(?, ?, f: 3.5, ..., p: $point);+$c = stuff(?, ?, ..., f: 3.5, p: $point);
 $c = fn(int $i, string $s, int $m = 0) => stuff($i, $s, 3.5, $point, $m); $c = fn(int $i, string $s, int $m = 0) => stuff($i, $s, 3.5, $point, $m);
  
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 // Prefill all params, making a "delayed call" // Prefill all params, making a "delayed call"
 $c = stuff(1, 'hi', 3.4, $point, 5, ...); $c = stuff(1, 'hi', 3.4, $point, 5, ...);
-$c = fn(...$args) => stuff(1, 'foo', 3.4, $point, 5, ...$args);+$c = fn(...$args) => stuff(1, 'hi', 3.4, $point, 5, ...$args);
  
 // Ex 12 // Ex 12
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 function stuff(int $i, string $s, float $f, Point $p, int $m = 0) {} function stuff(int $i, string $s, float $f, Point $p, int $m = 0) {}
  
-// Insufficient parameters.+// throws Error(not enough arguments and or place holders for application of stuff)
 $c = stuff(?); $c = stuff(?);
  
-// Parameter $i used more than once.+// throws Error(too many arguments and or place holders for application of stuff) 
 +$c = stuff(?, ?, ?, ?, ?, ?); 
 + 
 +// throws Error(Named parameter $i overwrites previous place holder)
 $c = stuff(?, ?, 3.5, $point, i: 5); $c = stuff(?, ?, 3.5, $point, i: 5);
  
-// Positional argument used after named argument.+// Fatal error: Named arguments must come after all place holders
 $c = stuff(i:1, ?, ?, ?, ?); $c = stuff(i:1, ?, ?, ?, ?);
  
 // Cannot use placeholder on named arguments. // Cannot use placeholder on named arguments.
 +// Parse error: syntax error, unexpected token "?"
 $c = stuff(1, ?, 3.5, p: ?); $c = stuff(1, ?, 3.5, p: ?);
  
-// Cannot use positional placeholder after named argument.+// Fatal error: Named arguments must come after all place holders
 $c = stuff(?, ?, ?, p: $point, ?); $c = stuff(?, ?, ?, p: $point, ?);
 </code> </code>
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 f(1, 2); f(1, 2);
  
-$f = f(?);+$f = f(?, ?);
  
 $f(1, 2); $f(1, 2);
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 For example: For example:
  
-<code>+<code php>
 function f(...$args) { function f(...$args) {
     print_r($args);     print_r($args);
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 $arrow = fn($who) => speak($who, getArg()); $arrow = fn($who) => speak($who, getArg());
-print "JOe\n";+print "Joe\n";
 $arrow('Larry'); $arrow('Larry');
  
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 ]; ];
  
-// $points is an array of 4 distinct Person instances. +// $people is an array of 4 distinct Person instances. 
-$points = array_map(new Person(?), $data);+$people = array_map(new Person(?), $data);
 </code> </code>
  
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-Magic methods ''__call'' and ''__callStatic'' are supported.  Specifically, creating a partial Callable off of a magic method will result in a callable with a signature consisting the number of arguments specified in the partial call, all with no type and named ''$args'' in reflection.+Magic methods ''%%__call%%'' and ''%%__callStatic%%'' are supported.  Specifically, creating a partial Callable off of a magic method will result in a callable with a signature consisting the number of arguments specified in the partial call, all with no type and named ''%%$args%%'' in reflection.
  
-Named arguments are also supported, the same as with ''__call'' natively, even though the name won't match reflection.+Named arguments are also supported, the same as with ''%%__call%%'' natively, even though the name won't match reflection.
  
 For example: For example:
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 $m(a: 1, b: 2); $m(a: 1, b: 2);
  
 +/* Prints:
 Foo::method Foo::method
 Array Array
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 </code> </code>
  
-The ''__get'' and ''__set'' magic methods are not called as methods, and thus there is no way to partially apply them.+The ''%%__get%%'' and ''%%__set%%'' magic methods are not called as methods, and thus there is no way to partially apply them.
  
 ===== Common use cases ===== ===== Common use cases =====
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 // $p is now a partially applied function with the same 4 arguments // $p is now a partially applied function with the same 4 arguments
 // as Foo::bar. Effectively there is no difference between now calling  // as Foo::bar. Effectively there is no difference between now calling 
-// $p(1, 2, 3, 4) and $foo->bar(1, 2, 3, 4).+// $p(1, 2, 3, 4) and $f->bar(1, 2, 3, 4).
 </code> </code>
  
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 ===== Syntax choices ===== ===== Syntax choices =====
  
-The ''?'' character was chosen for the placeholder largely because it was unambiguous and easy to implement.  Prior, similar RFCs (such as the original [[rfc:pipe-operator|Pipe Operator]] proposal from several years ago) used the ''$$'' sigil instead.  The RFC authors are open to considering other characters if they can be trivially swapped out, but would only support ''$$'' if it gets called ''T_BLING''.+The ''?'' character was chosen for the placeholder largely because it was unambiguous and easy to implement.  Prior, similar RFCs (such as the original [[rfc:pipe-operator|Pipe Operator]] proposal from several years ago) used the ''$$'' (lovingly called T_BLING) sigil instead.  So far no compelling argument has been provided for changing the character, so the RFC is sticking with ''?''.
  
 The ''...'' symbol was chosen for its similarity to variadic arguments.  They are conceptually similar, and thinking of ''...'' as the partial equivalent of ''...$args'' in a normal function is approximately accurate. The ''...'' symbol was chosen for its similarity to variadic arguments.  They are conceptually similar, and thinking of ''...'' as the partial equivalent of ''...$args'' in a normal function is approximately accurate.
 +
 +A few reviewers have suggested ''...?'' as an alternative variadic placeholder symbol, on the grounds that it is more-parallel with existing variadics.  However, Nikita Popov noted that would seem to imply it was a placeholder //for// a variadic, rather than a placeholder that is variadic.  Given that confusion, and that it entails a 33% increase in the number of characters needed for a common case, that alternative was rejected.
  
 ===== Excluded functionality ===== ===== Excluded functionality =====
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 None. None.
 +
 +===== Proposed Voting Choices =====
 +
 +As per the voting RFC a yes/no vote with a 2/3 majority is needed for this proposal to be accepted.
 +
 +The vote was opened on 16 June 2021 and closes 30 June 2021.
 +
 +<doodle title="Add partial function application PHP" auth="crell" voteType="single" closed="true">
 +   * Yes
 +   * No
 +</doodle>
  
 ===== Implementation ===== ===== Implementation =====
rfc/partial_function_application.1622654796.txt.gz · Last modified: 2025/04/03 13:08 (external edit)

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