Hi everybody,
doing some optimization on my code, I faced some strange question:
how to save a iota result in a class member?

Say I have
class A
{
    ??? member;

    auto testIter4()
    {
        return iota(0,5);
    }
}

void main()
{
    A a = new A();
    a.member = testIter4();
}

how would I declare the member?

What I found till now is this:
http://comments.gmane.org/gmane.comp.lang.d.learn/60129
where it is said, that I could use
inputRangeObject(testIter4)
and declare my member as InputRange!int

But then the random access is gone and, furthermore, looking into the source of std/range/interfaces.d found some lines (about line nr. 110) about performance and that the InputRangeObject has a performance penalty of about 3 times over using the iota struct directly. So, I could declare my member as typeof(iota(0))

Did I miss something?

As a comment on my own post:
I’m aware, that there are some different return types from functions like iota. And I’m also aware, that there are much less different range types. I can, maybe, define what kind of range type I want to have, the question is, how to map all the different function results to this one interface I need with as less performance penalty as possible

On Thursday, 24 March 2016 at 06:54:25 UTC, Alex wrote:
> Hi everybody,
> doing some optimization on my code, I faced some strange question:
> how to save a iota result in a class member?
>
> Say I have
> class A
> {
>     ??? member;
>
>     auto testIter4()
>     {
>         return iota(0,5);
>     }
> }
>
> void main()
> {
>     A a = new A();
>     a.member = testIter4();
> }
>
> how would I declare the member?
>

Yeah this is one of the downsides of voldermort types. In these cases typeof and ReturnType are your friend. It often takes me a couple of tries to get it right, but the following seems to work:

import std.traits : ReturnType;
import std.range : iota;
class A
{
    ReturnType!(A.testIter4) member;
    auto testIter4()
    {
        return iota(0,5);
    }
}

void main()
{

     A a = new A();
     a.member = a.testIter4();
	
}

On Thursday, 24 March 2016 at 08:13:27 UTC, Edwin van Leeuwen wrote:
> Yeah this is one of the downsides of voldermort types. In these cases typeof and ReturnType are your friend. It often takes me a couple of tries to get it right, but the following seems to work:
>
> import std.traits : ReturnType;
> import std.range : iota;
> class A
> {
>     ReturnType!(A.testIter4) member;
>     auto testIter4()
>     {
>         return iota(0,5);
>     }
> }
>
> void main()
> {
>
>      A a = new A();
>      a.member = a.testIter4();
> 	
> }

Ah... thanks! The "ReturnType" is what I looked for. This also makes some kind of semantic statement about "how slim should be the interface of my class members"...