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To: Larry Garfield <larry@garfieldtech.com>,
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References: <1ae611cb-b077-3db0-3237-c7ffa1c6e745@ralphschindler.com>
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 <e6eaa8f5-497b-1dec-ebee-bde26157bb06@ralphschindler.com>
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Date: Thu, 1 Jul 2021 11:55:29 -0500
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Subject: Re: [PHP-DEV] [Proposal] call_user_func_map(): flexible named
 parameter mapping for call_user_func*
From: ralph@ralphschindler.com (Ralph Schindler)


> What I don't understand is what the issue with that is?
> 
> You can already build up a named array and splat it into a function call to pass by name.  It's a really neat trick.  It doesn't need a dedicated function.
> 
> About a month ago, I went through all of TYPO3 and removed all remaining call_user_func_array() calls in favor of just $function(...$args), because it does the same thing and is faster, and easier to read.  Named arguments already work exactly that way, too.
> 
> I don't see an advantage to adding a function that does what you can already do with less syntax:
> 
> $args['foo'] = 5;
> $args['beep'] = get_value_from_db();
> $args['narf'] = 'poink';
> 
> $callable(...$args);
> 
> That works today in 8.0.  We're good.

The proposal focuses on the onus put on the author of the 
closure/function, not the caller.

If your $callable is only interested in $foo enforced as an int and 
$narf enforced as a string, what does the signature and body of the 
subscribing $callable look like in this case?

I am proposing that if a system is providing all of this for any 
registered callables:

   $args['foo'] = 5;
   $args['beep'] = get_value_from_db();
   $args['narf'] = 'poink';
   $args['boop'] = $boopObject;
   $args['isNoomable'] = false;

But are only interested in value for 'foo' and 'narf', they can still 
get type hinting/checking/enforcement and the benefits of named mapping.


Let's assume the following which has a little bit of context:

   // developer/consumer code
   $library = (new SomeLibrary)
   $library->registerCallback(function ($foo, $narf) {});
   $library->call();

   // some 3rd party library with a callback system in place
   class SomeLibrary {
     public function registerCallback(callable $callback) {
       $this->callback = $callback;
     }
     public function call() {
       if (!$this->callback) {
         return;
       }

       $args = [];
       $args['foo'] = 5;
       $args['beep'] = 'value from db';
       $args['narf'] = 'poink';
       $args['boop'] = new StdClass;
       $args['isNoomable'] = false;

       ($this->callback)(...$args);
     }
   }


This will fail with message:

   PHP Fatal error:  Uncaught Error: Unknown named parameter $beep in ...


Currently, the consumer/developer would have to write:

   $library->registerCallback(function (...$args) {
     $foo = $args['foo'];
     $narf = $args['narf'];
     // ...
   });

   // or
    $library->registerCallback(function ($foo, $beep, $narf, $boop, 
$isNoomable) {
     // do something with foo or narf
   });


Additionally, the library/framework is now precluded from adding new 
parameters since any consuming callables would also have to introduce 
these new parameters as it could be considered a BC break.

The more I think about it though, the more sensible this would be as it 
allows the callback provider to opt into named parameter mapping 
destructuring:


   $library->registerCallback(function (...[string $foo, string $narf]) {
     // do something with $foo and $narf
   });


-ralph