Synax for variadic template

[Nicholas Wilson via Digitalmars-d-learn]

On Friday, 1 September 2017 at 09:38:59 UTC, Alex wrote:
> Hi all!
> Say, I have
>
> struct A(T...)
> {
> 	T arr;
> }
>
> struct B(T...)
> {
> 	T[] arr;
> }
>
> void main()
> {
> 	A!(int[], double[]) a;
> 	a.arr[0] ~= 5;
> 	a.arr[0] ~= 6;
> 	static assert(!__traits(compiles, a.arr[0] ~= 3.5));
> 	a.arr[1] ~= 19.8;
> 	
> 	assert(a.arr[0] == [5,6]);
> 	assert(a.arr[1] == [19.8]);
> 	assert(a.arr[1].length == 1);
> 	assert(a.arr[0].length == 2);
> 	
> 	B!(int, double) b;
> 	//b.arr[0] ~= 5;
> }
>
> While struct A behaves like expected, how to get by with B?
> What I want is just to abstract the array property out of 
> template arguments...
>
> Thanks in advance :)

b.arr refers to an `(AliasSeq!(int, double))[]`, so with 
`b.arr[0] ~= 5;` you are trying to append a integer to an array 
of pairs of ints and doubles, which you can't do.

b.arr[0] ~= ElementType!(typeof(b.arr))(5,42.0);

should work (I hope, not tested) but you cannot append only the 
int.

If you are trying to abstract the array for struct of array vs. 
array of struct the take a look at 
https://maikklein.github.io/post/soa-d/