named arguments (C++) - Something D could learn from

[aliak]

On Tuesday, 18 December 2018 at 11:15:26 UTC, Simen Kjærås wrote:
> On Tuesday, 18 December 2018 at 11:08:43 UTC, aliak wrote:
>>> It's not even fewer characters! It's not trivial but it's 
>>> possible to make the order not matter by using a templated 
>>> implementation and aliasing it to `displayCoolName`.
>>
>> You also have to build it:
>>
>> func toHex(r: Int, g: Int, b: Int) -> Int {
>>   return r << g << b;
>> }
>>
>> As opposed to:
>>
>> struct R {
>>   int value;
>> }
>> struct G {
>>   int value;
>> }
>> struct B {
>>   int value;
>> }
>> int toHex(R r, G g, B b) {
>>   return r.value << g.value << b.value;
>> }
>>
>> That's 67 vs 146 characters. Not to mention one pollutes the 
>> namespace and one doesn't.
>
> No need to pollute the namespace:
>
> struct args {
>     template opDispatch(string name) {
>         alias opDispatch = Arg!name;
>     }
> }
>
> struct Args(T) {
>     template opDispatch(string name) {
>         alias opDispatch = Arg!(name, T);
>     }
> }
>
> struct Arg(string name) {
>     static auto opAssign(T)(T value) {
>         return Arg!(name, T)(value);
>     }
> }
>
> struct Arg(string name, T) {
>     T value;
>     alias value this;
> }
>
> void fun(Args!int.foo foo) {} // Unfortunately requires 
> repetition of arg name. :(
>
> unittest {
>     fun(args.foo = 3);
> }
>
> --
>   Simen

Woah... that's quite neat.

I feel like this is how std.typecons.Flag should have been made!!

I played around with it for a bit, and if there was a way to get 
some better error messages then that could be quite nice to use! 
- i dunno, maybe through some static assert on the "string 
names"s being passed in or something...

Cheers,
- Ali