Gotcha with const std.range.chunks

H. S. Teoh hsteoh at
Thu Jul 30 19:15:36 UTC 2020

On Thu, Jul 30, 2020 at 06:52:42PM +0000, sportsracer via Digitalmars-d-learn wrote:
>     int[] xs = new int[100];
>     const chunked = xs.chunks(10);
>     writeln(chunked[0][0]);
> }
> Error: mutable method std.range.Chunks!(int[]).Chunks.opIndex is not
> callable using a const object

In order to iterate the chunks, you must be able to mutate the range
object returned by .chunks. If it's const, then it's not mutable, and
therefore it cannot be iterated.

If you want to protect the underlying data from mutation, create a const
view of the data first, e.g., something like this:

	int[] xs = new int[100];
	const(int)[] constView = xs;
	auto chunked = constView.chunks(10); // N.B. mutable

The range itself will be mutable, but the elements will be const and not
mutable through the range.


Why can't you just be a nonconformist like everyone else? -- YHL

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