Pretty please: Named arguments

[Jason E. Aten]

I find this an interesting discussion.  Coming from writing alot of code in
language that makes extensive and
highly effective use of named arguments (R), I can say that optional named
arguments
(as in Lisp, and descendants like Python and R) do have big software
engineering benefits,
but also come with a substantial costs in terms of complexity of the
function call sequence.

That is, named arguments can be expensive in a typical interpreted
implementation
(probably one reason why R and Python are much slower to execute than the
other
interpreted languages), presumably because each function call has to
invoke hash
table lookups to determine the canonical formal position of each actual
argument, and deal with variadic
cases, to rearrange the order of the arguments to match expectations of the
callee.

Someone familiar with lisp compilers could probably tell you if the heavy
speed tax is intrinsic
or just the price of interpretation.

It would indeed be an interesting challenge to see if the compile-time
metaprogramming
features of D would allow one to include named arguments in an opt-in
fashion without speed reduction.

Jason

On Wed, Mar 2, 2011 at 6:16 AM, Don <nospam at nospam.com> wrote:

> Jim wrote:
>
>> Jonathan M Davis Wrote:
>>
>>  On Tuesday, March 01, 2011 11:22:17 Bekenn wrote:
>>>
>>>> On 2/28/11 1:38 PM, Don wrote:
>>>>
>>>>> 1. It makes parameter names part of the API.
>>>>>
>>>> I wrote earlier that this would probably be the first time parameter
>>>> names "leaked" into user code, but I was wrong.  Jacob Carlborg has
>>>> pointed out his library implementation of this feature:
>>>>
>>>> http://dsource.org/projects/orange/browser/orange/util/Reflection.d#L135
>>>>
>>>> If you look through his implementation, you'll see that it uses the
>>>> .stringof property to extract parameter names from the function
>>>> definition.  In essence, parameter names are /already/ part of the API,
>>>> because code can be written that depends on them.  And the fact that a
>>>> library implementation exists specifically to facilitate the use of
>>>> named arguments implies that code already /has/ been written that
>>>> depends on parameter names.
>>>>
>>>> Like it or not, parameter names are already part of the API.  Adding
>>>> named arguments as a language feature doesn't change that.
>>>>
>>> You're talking about a third party library that's trying to hack in named
>>> arguments, not the language nor the standard library.
>>>
>>> The parameter names of a function are _not_ currently part of its
>>> signature. You could have a .di file without any parameter names or with
>>> totally different parameter names than the original .d file and it would
>>> have _zero_ effect on anything calling those functions. The function
>>> signature does _not_ include the name of its parameters - just their types.
>>> Adding named arguments would change that.
>>>
>>> - Jonathan M Davis
>>>
>>
>>
>> Neither are aliases signatures but they can still be imported. If the
>> library writer choose to expose argument names in the .di file then I'd say
>> they are part of the API.
>>
>
> The library writer has no choice.
> Templates function implementation must be included in the .di file. This
> exposes the parameter names.
>
> The proposal introduces additional coupling between library code and user
> code, which is useless in the majority of cases.
>
> I can see the value in an opt-in annotation (*not* opt-out) for those
> problem domains where large numbers of function parameters are normal. But I
> would strongly oppose it in general.
>
>
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