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Date: Thu, 21 Oct 2010 10:52:27 +0300
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Subject: Re: [PHP-DEV] Skipping of defaulted parameters.
From: ionut.g.stan@gmail.com ("Ionut G. Stan")

On 20/Oct/10 2:58 PM, Richard Quadling wrote:
> Hello.
>
> Take the following simple code.
>
> <?php
> function foo($var1, $var2 = 2, $var3 = 3) {
>   echo "$var1, $var2, $var3\n";
> }
>
> foo(10); // 10, 2, 3
> foo(10, 20); // 10, 20, 3
> foo(10, 20, 30); // 10, 20, 30
> foo(10, null, 30); // 10, , 30
> foo(10,, 30); // Parse error.
> ?>
>
> According to the manual
>
> A variable is considered to be null if it has not been set to any value yet [1].
> By default, function arguments are passed by value [2].
> When using default arguments, any defaults should be on the right side
> of any non-default arguments. [3]
>
>
>  From this, the question I have is what do I pass when I want to use
> the default, WITHOUT having to supply the default value itself.
>
> On the surface, null should work. Null (according to [1]) is
> specifically saying that there is no value. But it is being
> interpreted as a value.
>
> I'm guessing the reason for null being interpreted as a value is
> really that the supplied argument count is used and any unsupplied
> arguments are defaulted.
>
> But null isn't a value ... that seems to be REALLY important to me.
> But from userland it is a value. Just a really odd one.
>
> I would argue that by having a null in the arguments, the intent is to
> NOT supply a value and have the default value used in the function.
>
>
> Possible solutions.
>
> 1 - Do nothing in core and implement is_null() checking to reinstate
> the default value.
>
> function foo($var1, $var2 = 2, $var3 = 3) {
>   $var2 = is_null($var2) ? 2 : $var2;
>   $var3 = is_null($var3) ? 3 : $var3;
>   echo "$var1, $var2, $var3\n";
> }
>
>
> 2 - Allow null to be supplied and have the default value be used for
> the argument.
>
> foo(10, null, 30); // would output 10, 2, 30
>
>
> 3 - New keyword of default or void to specifically indicate the intent
> to use the default value for the argument.
>
> foo(10, default, 30); // would output 10, 2, 30
>
>
> 4 - Allow missing arguments to default.
>
> foo(10,, 30); // Parse error.
>
>
>
> Option 4 would probably be the worse one to go for. Looking any number
> of languages that support defaults and you will see code like ...
>
> someFunction(param1,,,,,param7,,,,param11)
>
> sort of thing.
>
>
>
> Option 3, whilst does clearly indicate the intent, does introduce a
> new keyword. As a non core dev, I'm guessing we end up with naming
> conflicts. And something called "default" is probably going to be a
> big one. "Void" also.
>
> But using something like _ (yep, underscore), could be a solution here [4].
>
>
>
> Option 2, after probably having to reject option 3, would be my
> choice. I want null to REALLY mean nothing. Just like it would be in
> foo(10).
>
>
>
> Option 1 is what I have to do at the moment.

Option 5: Implement named parameters?

-- 
Ionuț G. Stan  |  http://igstan.ro