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Date: Wed, 23 Jun 2004 20:01:51 +0000 (GMT)
To: Bert Slagter <bert@procurios.nl>
cc: internals@lists.php.net
In-Reply-To: <20040623163305.73484.qmail@pb1.pair.com>
Message-ID: <20040623194751.N22728@hyperion-data.net>
References: <20040623150429.E62456@hyperion-data.net> <20040623163305.73484.qmail@pb1.pair.com>
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Subject: Re: [PHP-DEV] Re: keyword arguments?
From: daniel@hyperion-data.net (Daniel Crookston)

The major benefit of keyword arguments doesn't occur when you're writing 
functions, it occurs when you're re-writing them.  I can't count the 
number of times where I've thought "My xyz function already does something 
almost exactly like what I need... if I just passed it an extra parameter, 
I could rewrite xyz to do what I need and save a lot of time."  So I add 
another parameter, making it optional.

This is fine, all the calls to xyz that are lacking the final parameter 
still work (since it's optional.)  But do this once or twice, and pretty 
soon you have function calls that look like this:

xyz('a', 2, $foo, '', '', '', '', '', '', $bar);

That's ugly and unnecessary, and leaves lots of room for bugs when you're 
writing functions that use the nth optional parameter in your function 
(since you have to count the number of blank spaces you need to leave.)

Additionally, what happens when all of your original, three-argument (a, 
2, $foo) calls to xyz need to start passing an additional argument because 
of a change you couldn't predict when you first wrote your function?

Keyword arguments solve these problems.  They're always optional - not 
just optional in that you can stick a '' or NULL in the spot where you 
would put a value in the function call.  They're optional in that you can 
leave them out entirely.  Because they're named, they can also be passed 
in any order.  And, finally, you can add new keyword arguments at any 
time, and none of your current function calls will break.

If there's a way to do this in PHP (short of having the last argument be a 
hash) that I've missed, please let me know about it.

Daniel Cr

On Wed, 23 Jun 2004, Bert Slagter wrote:

> Even after reading your message twice, I can't think of an example where this 
> would be useful. Obviously, I don't understand your intention.
>
> Could you give an example of a construction that is made possible by this 
> feature (and thus would otherwise be impossible)?
>
> Bert