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Date: Thu, 19 Apr 2012 09:33:12 -0400
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Subject: Re: [PHP-DEV] Re: [RFC] skipping optional parameters
From: weierophinney@php.net (Matthew Weier O'Phinney)

On 2012-04-19, Patrick ALLAERT <patrickallaert@php.net> wrote:
> 2012/4/18 Matthew Weier O'Phinney <weierophinney@php.net> :
> > My one comment, which others have raised, is readability of multiple
> > commas -- TBH, at first glance it has the appearance of a mistake. I
> > think those suggesting a keyword such as "default" make a good point in
> > this regard -- it makes it 100% clear that you want the default value
> > for the argument in that position. This also presents an improvement
> > over current usage, as you're not hard-coding values in your function
> > calls themselves -- particularly as the defaults could change in future
> > refactors.
>
> I think we should only support optional parameters using the "default"
> keyword as it would probably make things more consistent and less
> error prone:
>
> function foo( $bar = "bar", $foo = "foo", $baz = "baz" ) { ... }
>
> foo(,,, "myBaz"); // Thinking changing the value of $baz, but there's
> one too much "," and PHP won't complain because of too many arguments
> used!
>
> Additionally, we might also want to think about
> call_user_func()/call_user_func_array().
>
> If for the former it could work with:
>
> call_user_func( "foo", , , "myBaz" );
>
> What about the latter?
>
> call_user_func_array( "foo", [2 => "myBaz"] ); // ? Evaluating the
> element at index 0 would cause a notice, but would result in a NULL,
> so I would say that NULL is to be used as first parameter.

I actually would argue you shouldn't skip parameters when using
call_user_func(); even with call_user_func_array(), I'd argue that named
parameters is the only way I'd want to allow skipping parameters.

The reason I argue this is because when dynamically calling a function,
you typically don't actually know exactly what the function/method is --
and thus making any assumptions about the signature other than required
parameters is simply begging for problems.

<snip>

> Last but not least: if skipping optional parameters is implemented,
> should we consider the support of default values on the leftmost side
> of functions?
>
> function foo( $bar = "bar", $baz ) { ... }
>
> It could make sense that $bar followed by $baz is semantically better
> than the opposite for technical reason, and this could be called
> using:
>
> foo( default, "baz")
> or:
> foo(, "baz")

I'd argue no -- as required arguments should always have precedence over
optional ones in the signature when it comes to position.

-- 
Matthew Weier O'Phinney
Project Lead            | matthew@zend.com
Zend Framework          | http://framework.zend.com/
PGP key: http://framework.zend.com/zf-matthew-pgp-key.asc