Ranges seem awkward to work with

[Mike Parker via Digitalmars-d-learn]

On Tuesday, 12 September 2017 at 01:13:29 UTC, Hasen Judy wrote:
> Is this is a common beginner issue? I remember using an earlier 
> version of D some long time ago and I don't remember seeing 
> this concept.
>
> Now, a lot of library functions seem to expect ranges as inputs 
> and return ranges as output.
>
> Even parsing a csv line returns a range. And the funny thing 
> is, once you loop over it, it's done. You've basically consumed 
> it.
>
> For example, I was having some trouble with the api of the 
> std.csv module, so to help me debug, I printed the result of 
> the csv. ok, the result seems good. Now I try to use it, for 
> example:
>
>     auto name = row[1];
>
> And to my surprise there's a runtime error, something about 
> range something something. I don't even remember what the error 
> was. The thing is, it wasn't clear what was going on.
>
> The line was actually more like:
>
>         auto some_var = 
> some_function(row[1].some_other_library_method!template_variable);
>
> So because I was calling several library methods on the same 
> line, I thought the problem might have something to do with the 
> range not exactly matching what the library was expecting. I 
> thought maybe row[1] also returned some range instead of a 
> string and that range had something wrong with it.
>
> Well, it turned out that my earlier attempt to print the parsed 
> csv row resulted in the row being "consumed" and now the row is 
> an empty range(!).
>
> Is there a straight forward way to convert a Range to a list 
> other than manually doing a foreach?
>
>     string[] items;
>     foreach(item; someRangeThing) {
>         items ~= item;
>     }
>
> I feel like that is a bit of an overkill.

Don't think of ranges as persistent containers. They aren't. They 
are transient entities, temporary views of data. If you have a 
container and want a consumable view of it that doesn't mutate 
the container itself, produce a range. If you receive a range and 
want to transform it from a transient entity into something 
concrete, use std.array.array or a range-based container API. If 
it helps, Chapter 6: Understanding Ranges from 'Learning D' is 
available (in somewhat mutilated form) as an article at the 
publisher's site:

https://www.packtpub.com/books/content/understanding-ranges