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Date: Sun, 27 Jun 2021 10:39:10 -0400
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Subject: [Proposal] call_user_func_map(): flexible named parameter mapping for
 call_user_func*
From: ralph@ralphschindler.com (Ralph Schindler)

The short proposal:


Make a variation of this work (notice parameter order and 'b' is goes 
unused):

     call_user_func_map(
       fn ($c, $a) => var_dump($a, $c),
       [
         'a' => 'the a value',
         'b' => 'the b value',
         'c' => 'the c value'
       ]
     );

     // string(11) "the a value"
     // string(11) "the c value"




The long proposal:


Callables, Closures, Anon Funcs, etc - have enjoyed increasing 
popularity year over year. We've even gotten a shorter syntax for them 
`fn ()` and more RFC's are sure to be on their way.

This proposes a method for a publisher/framework/producer (the caller of 
the callback) to document all the parameters that are available as named 
parameters, and subscribers/consumers (creator of the callback) could 
subscribe to what they need by name.

For example:

     // documented callback parameters, this is what is available:
     $params = [
       'a' => 'value for a',
       'b' => 'value for b',
       'c' => 'value for c'
     ];

     // a consumer only interested in $a and $c could write:
     $f = fn ($c, $a) => var_dump($a, $c);

The consumer would then register their callback with the 
producer/framework/etc or pass as the parameter to whatever is consuming it

     $callbackSystem->register('some_event', $f)

     // or

     $doSomething->with($f);

The framework could then call with success:

     call_user_func_map($usersCallable, $allAvailableNamedParameters);


Currently the only way to do this is through array_diffing parameters 
found via Reflection, then passing them along to call_user_func_array() 
as a named array.

Attempting to use call_user_func_array() without specifying all provided 
variables results in:

     Uncaught Error: Unknown named parameter X in ...

Thoughts?