Thread overview
Ranges seem awkward to work with
September 12
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.
September 12
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.

if `range.save` works use that, otherwise

`range.dup` will duplicate the range

or `range.array` (from std.array) will enumerate the range into an array (which is pretty much the same as your solution above.
September 12
On Tuesday, 12 September 2017 at 01:18:21 UTC, Nicholas Wilson wrote:
> On Tuesday, 12 September 2017 at 01:13:29 UTC, Hasen Judy wrote:
>> Is this is a common beginner issue?
>
> if `range.save` works use that, otherwise

std.csv does not, IIRC.

>
> `range.dup` will duplicate the range

That isn't a range property.


> or `range.array` (from std.array) will enumerate the range into an array (which is pretty much the same as your solution above.

This. Ranges are great in part because they are often lazy, a sequence of operations can be defined but only executed when used. Some operations need the whole collection, eg sort.
September 12
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.
>

D's ranges can take getting used to, so if you haven't already, these two articles are worth the read to get familiar with them imho [1][2].
One way to look at it is that input ranges (empty,front,popFront) model iteration of the elements of some data source (another is that they model a monotonic advancing data source).

[1] http://www.drdobbs.com/architecture-and-design/component-programming-in-d/240008321
[2] https://wiki.dlang.org/Component_programming_with_ranges
September 12
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
September 12
On Tuesday, 12 September 2017 at 01:13:29 UTC, Hasen Judy wrote:
> Now, a lot of library functions seem to expect ranges as inputs and return ranges as output.

Unless I'm mistaken, it was done on purpose to reduce the amount of memory allocations in the standard library so that it becomes @nogc-friendly. But yes, you can use std.array.array to turn it into an array, but keep in mind that it does allocate so you might need to watch out if you're dealing with large CSV files.
September 13
On Tuesday, September 12, 2017 13:47:47 Azi Hassan via Digitalmars-d-learn wrote:
> On Tuesday, 12 September 2017 at 01:13:29 UTC, Hasen Judy wrote:
> > Now, a lot of library functions seem to expect ranges as inputs and return ranges as output.
>
> Unless I'm mistaken, it was done on purpose to reduce the amount of memory allocations in the standard library so that it becomes @nogc-friendly. But yes, you can use std.array.array to turn it into an array, but keep in mind that it does allocate so you might need to watch out if you're dealing with large CSV files.

Ranges were a big thing in Phobos years before @nogc came along. They're used because they're an extremely powerful idiom. I don't even recall much in the way of discussions related to their efficiency vs arrays early on. That did come later, and ranges have significantly helped the memory efficiency of D programs regardless of @nogc, but that really wasn't the motivating factor. And even now, a lot of the basic uses of ranges _do_ allocate, because they use lambdas that end up with closures being allocated for them (which uses far less memory than allocating a dynamic array but is not @nogc). That can be avoided by doing stuff like using static nested functions or functors, but your average rangd-based code doesn't tend to jump through those hoops.

Ranges do take some getting used to, but we have them precisely because they're so flexible and powerful.

- Jonathan M Davis