Function parameters from TypeTuple

[Tofu Ninja via Digitalmars-d-learn]

On Friday, 17 October 2014 at 19:03:42 UTC, anonymous wrote:
> On Friday, 17 October 2014 at 17:57:58 UTC, Tofu Ninja wrote:
>> On Friday, 17 October 2014 at 17:44:48 UTC, Tofu Ninja wrote:
>>
>> Not sure if what I wrote made sense, instead I will just post 
>> the code that is vomiting on me...
>
> You forgot the imports.
>
>> template arrayType(T)
>> {
>> 	alias arrayType = T[];
>> }
>>
>> template multiAccess(Args ...)
>> {
>> 	auto multiAccess(int i, staticMap!(arrayType, Args) args)
>> 	{
>> 		static if(args.length == 1) return Tuple!(args[0][i]);
>
> `Tuple` is a type template. Use `tuple(foo, bar)` to build a
> `Tuple!(typeof(foo), typeof(bar))`.
>
> => return tuple(args[0][i]);
>
>> 		else return Tuple!(args[0][i], multiAccess!(Args[1 .. 
>> $])(args[1 .. $]));
>
> `Tuple!` -> `tuple` again. Also, `multiAccess` needs `i` again.
> And you want to `expand` the sub-result into the tuple so that
> it's flat.
>
> => return tuple(args[0][i], multiAccess!(Args[1 .. $])(i, args[1
> .. $]).expand);
>
>> 	}
>> }
>>
>> void main(string[] args)
>> {
>> 	int[] a = [1,2];
>> 	int[] b = [5,6];
>> 	writeln(multiAccess!(int,int)(1, a,b));
>> }
>>
>> but the compiler really does not like that at all... the error 
>> message are very unhelpful as well...
>>
>> Generates 18 errors...
>>
>> main.d(52): Error: variable _param_1 cannot be read at compile 
>> time
> [...]
>
> This is about you trying to instantiate `Tuple` with the runtime
> value that is `args[0][1]`.
>
>> main.d(52): Error: tuple index 0 exceeds length 0
> [...]
>
> I don't know where these come from. They don't show up for me.
>
>> main.d(53): Error: template instance main.multiAccess!() error 
>> instantiating
> [...]
>
> These are due to previous errors.
>
>
> For style points you could
>
> * Use the short form for function templates:
>
>      auto multiAccess(Args ...)(int i, staticMap!(arrayType, 
> Args)
> args) {...}
>
> * Take array types as template arguments instead of constructing
> them. This allows them to be inferred (IFTI - Implicit Function
> Template Instantiation):
>
>      auto multiAccess(Args ...)(int i, Args args)
>          /* Maybe put a template constraint here that forces 
> Args
> to be all arrays. */
>      {
>          import std.typecons: tuple;
>          static if(args.length == 1) return tuple(args[0][i]);
>          else return tuple(args[0][i], multiAccess(i, args[1 ..
> $]).expand);
>      }
>      void main()
>      {
>          int[] a = [1,2];
>          int[] b = [5,6];
>          import std.stdio;
>          writeln(multiAccess(1, a,b));
>      }

I had the imports, I just didn't post them. My problem is most 
likely that I used Tuple! instead of tuple... which is probably 
because the differences between the like 20(exaggeration) 
different types of tuples in D are confusing as hell...