Something to extend an array with a lazy range

[dlangBugzillaToGithub]

bearophile_hugs reported this on 2013-05-26T06:14:15Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=10176

CC List

• andrej.mitrovich (@AndrejMitrovic)
• issues.dlang (@jmdavis)

Description

Maybe it's worth adding a std.array.extend() function that's similar to "~=" but accepts a lazy range (in theory, in a language where ranges are built-ins, ~= should append ranges too to arrays).

In std.array there is a join, but it creates a whole new array. It's usually more efficient to extend arrays.


foreach (x; myrange)
    myarray ~= x;


Is replaced by:

myarray.extend(myrange);

[dlangBugzillaToGithub]

andrej.mitrovich (@AndrejMitrovic) commented on 2013-05-26T06:21:09Z

Hmm, I would have hoped that 'put' would work here, but it doesn't:

-----
import std.range;
import std.array;

void main()
{
    {
        Appender!(int[]) arr;
        arr.put(iota(5));  // ok
        assert(arr.data == [0, 1, 2, 3, 4]);
    }

    {
        int[] arr;
        arr.put(iota(5));  // runtime exception
        assert(arr == [0, 1, 2, 3, 4]);
    }
}
-----

> core.exception.AssertError@C:\dmd-git\dmd2\windows\bin\..\..\src\phobos\std\array.d(587): Attempting to fetch the front of an empty array of int

[dlangBugzillaToGithub]

bearophile_hugs commented on 2013-05-26T13:12:23Z

More general issue summary.

[dlangBugzillaToGithub]

issues.dlang (@jmdavis) commented on 2013-05-26T17:22:46Z

> Hmm, I would have hoped that 'put' would work here, but it doesn't:

put on arrays does not append. It starts writing at the beginning of the array. So, it functions fundamentally differently from most output ranges. Presumably, it's the desired behavior if you're dealing with a pre-allocated chunk of memory that you're trying to fill, but it is problematic in that it doesn't function like other output ranges. I've been think of opening a discussion in the newsgroup on it so that we can figure out how to better sort out some of these quirks of output ranges.

[dlangBugzillaToGithub]

andrej.mitrovich (@AndrejMitrovic) commented on 2013-05-27T02:06:50Z

(In reply to comment #3)
> > Hmm, I would have hoped that 'put' would work here, but it doesn't:
> 
> put on arrays does not append. It starts writing at the beginning of the array.

That makes sense now that I think about it.