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Date: Wed, 17 Sep 2014 18:23:02 +0100
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Subject: Re: [PHP-DEV] [RFC] Implicit isset() in Shorthand Ternary Operator
From: rowan.collins@gmail.com (Rowan Collins)

Matthew Fonda wrote (on 17/09/2014):
> Hi Andrea,
>
> This is great -- thanks to you and Nikita for the work here.
>
> Syntax wise, I would prefer a function-like syntax, e.g. coalesce($a, $b,
> 'c') or ifsetor() instead of $a ?? $b ?? 'c'. I find this more readable,
> and it avoids any possible confusion about precedence within the
> expressions. Either way, still +1 for this feature.

Funnily enough, the standard library at my workplace has long included a 
coalesce() function as below, which is indeed very handy; there is also 
a coalesce_empty(), which calls empty($arg) instead of is_null($arg). 
Both pre-date the shorthand ?: operator, which could replace 
coalesce_empty(); the proposed ?? could replace coalesce()

As mentioned in the PHPDoc, the downside of a function is that it can't 
short-cut evaluation if the first argument passes, whereas an operator 
can. It would be possible to work around this by defining a special 
"language construct" rather than a real function, but that's probably 
more confusing than it's worth.

The special case for $first is a performance optimisation because 
func_get_args() has rather a lot of overhead; I'm guessing 5.6's 
variadic signatures ($args...) are less painful (can anyone confirm?)

/**
  * coalesce
  * PHP analogue of the SQL Coalesce() function
  * @param an arbitrary number of arguments
  * @return the first argument which is not NULL; If all arguments are 
NULL, will return NULL
  *
  * coalesce( $a, $b ) is equivalent to ($a === NULL ? $a : $b)
  * but coalesce( hard_work(), 'default' ) only has to do hard_work() once
  * [OTOH, coalesce( $a, hard_work() ) has to do hard_work() even if the 
result gets thrown away]
  */
function coalesce($first)
{
     if (!is_null($first))
     {
         return $first;
     }

     foreach ( func_get_args() as $arg )
     {
         if ( ! is_null($arg) )
         {
             return $arg;
         }
     }
}

-- 
Rowan Collins
[IMSoP]