Pretty please: Named arguments

[Jonathan M Davis]

On Monday, February 28, 2011 14:25:05 Bekenn wrote:
> On 2/28/11 1:38 PM, Don wrote:
> > spir wrote:
> >> On 02/28/2011 07:51 PM, Jonathan M Davis wrote:
> >>> I'm not entirely against named arguments being in D, however I do
> >>> think that any
> >>> functions that actually need them should be refactored anyway.
> > 
> > I agree.
> > CreateFont() in the Windows API, I'm looking at you. (For Linux people,
> > that function has about 12 parameters).
> 
> That's a great example of where named parameters can come in very handy.
>   As a consumer of the API, you do not have the option of refactoring
> CreateFont(); you have to play the cards you're dealt.  Named arguments
> allow you to annotate in a compiler-verified fashion.
> 
> >> Just don't use them!
> > 
> > You don't have that option. At least, if you're a library developer, you
> > don't. (I'm a bit sick of people saying "you don't have to use it if you
> > don't want to" in language design. If it is in the language, you don't
> > have a choice. You will encounter it).
> 
> You may encounter it, but nothing says you ever have to write it.  There
> is no way to write a function such that callers would have to use named
> arguments in the function call.  (If there were, then I'd agree with you
> -- that would be bad.)
> 
> > There are a couple of things that I really, really don't like about the
> > names argument idea:
> > 1. It makes parameter names part of the API.
> > Providing no way for the function writer to control whether it is part
> > of the API or not, and especially, doing it retrospectively, strikes me
> > as extremely rude.
> 
> A valid point.  I think I would already consider parameter names to be
> part of the API, though; generated documentation relies upon them, as do
> contracts.  Admittedly, this would be the first place where they leak
> directly into caller code.

And that's a _big_ problem. For instance, how many parameter names in Phobos 
were chosen with the idea that a caller would use them? _None_. And now, if 
named arguments are added, all of a sudden, you can't rename parameters without 
breaking code. I, for one, do not want to _increase_ the number of things that I 
can't change in code without breaking other people's code.  And at least with 
functions, I could rename them and leave a deprecated alias. With parameters, I 
don't have that option. A poorly named parameter would be set in stone unless 
the whole function were renamed or we were willing to break other people's code. 
Named arguments _decrease_ flexibility as far as the API goes.

On top of that, we would then have to worry about having high consistency in 
parameter names instead of just in function names. From the perspective of the 
library writer, this causes _more_ problems at _no_ benefit. From the perspective 
of the library user, it does provide some benefit, but I honestly do not think 
that

func(x : 4, y : 5);

is easier to read than

func(4, 5);

Sure, you have to know what func's parameters are, but you have to know that 
anyway. Only now, with named arguments, you have to care about what their 
_names_ are in addition to what they're for. I do _not_ want to have to read 
code which uses named arguments. It's just more clutter and more intellectual 
overhead.

The sole type of case that I have seen where named arguments are of real benefit 
is where you're dealing with horribly written functions that have a ton of 
parameters, and I would _hope_ that that kind of nonsense would be restricted to 
old C APIs and the like. And if you have to deal with such C APIs from D, you 
can write a wrapper which uses a proper struct or whatnot to encapsulate that 
mess. Such horrendous functions shouldn't be the norm at all.

As a library user, I see little benefit to named arguments and a definite problem 
with them in terms the added code clutter and intellectual overhead. As a 
library writer, it gives me _no_ benefit and definitely makes my life harder. 
Parameter names have never been part of a function's signature, and I _don't_ 
want them to start being a part of it now.

The more I think about this, the more I'm against the idea of named arguments.

- Jonathan M Davis