Re: Iterators in structs

[Paul Backus via Digitalmars-d-learn]

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);

Iterators in structs

[repr-man via Digitalmars-d-learn]

As an extension of my previous thread 
(https://forum.dlang.org/thread/nupwljahyutnyxdvp...@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!