June 25, 2020 Iterators in structs | ||||
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As an extension of my previous thread (https://forum.dlang.org/thread/nupwljahyutnyxdvpxob@forum.dlang.org), I wanted to ask about iterators in structs. I will start with the following code: void main() { int[5] a = [0, 1, 2, 3, 4]; int[5] b = [5, 6, 7, 8, 9]; auto x = ChunksOf(chain(a[], b[]), 2); } struct ChunksOf { this(R)(R r, size_t width) { auto iter = r.chunks(width); assert(is(typeof(iter) == Chunks!R)); } } This code works as expected. However, if the struct changes to: struct ChunksOf { Chunks!R iter; this(R)(R r, size_t width) { this.iter = r.chunks(width); assert(is(typeof(iter) == Chunks!R)); } } it doesn't compile because R is only in the scope of the constructor. This leads me to change the struct to: struct ChunksOf(R) { Chunks!R iter; this(R r, size_t width) { this.iter = r.chunks(width); assert(is(typeof(iter) == Chunks!R)); } } This works, only if I change the declaration of x in main() to: auto x = ChunksOf!(chain(a[], b[]))(chain(a[], b[]), 2); This requires me to pass the iterator as a template parameter and a regular parameter. Since this is a bit redundant, and I wanted to know if there was a better way to do it. Thanks for the help! |
June 25, 2020 Re: Iterators in structs | ||||
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Posted in reply to repr-man | On Thursday, 25 June 2020 at 18:47:42 UTC, repr-man wrote:
> struct ChunksOf(R)
> {
> Chunks!R iter;
>
> this(R r, size_t width)
> {
> this.iter = r.chunks(width);
> assert(is(typeof(iter) == Chunks!R));
> }
> }
>
> This works, only if I change the declaration of x in main() to:
>
> auto x = ChunksOf!(chain(a[], b[]))(chain(a[], b[]), 2);
>
> This requires me to pass the iterator as a template parameter and a regular parameter. Since this is a bit redundant, and I wanted to know if there was a better way to do it.
>
> Thanks for the help!
The usual solution is to create a helper function:
ChunksOf!R chunksOf(R)(R r, size_t width)
{
return ChunksOf!R(r, width);
}
The compiler can infer template arguments for function calls, so you can call it like this:
auto x = chunksOf(chain(a[], b[]), 2);
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