Gotcha with const std.range.chunks

sportsracer steffenwenz+d at
Fri Jul 31 15:37:22 UTC 2020

Right, thank you! The range object needs to be mutated to be 
iterated on, that explains it.

Although it looks like the opIndex on this particular range could 
guarantee constness:

Here's a longer code snippet that gives some context on why I 
thought I needed a const range object. This Matrix class would 
have the chunks range object stored as a private property, and 
use it in its opIndex to look up values. I wanted to add the 
const qualifier to the opIndex method, since it doesn't mutate 
the Matrix state, and that's what surfaced this error.

class Matrix(T)
     private {
         T[] data;
         Chunks!(T[]) view;

     this(size_t width, size_t height)
     { = new int[width * height];
         this.view = data.chunks(width);

     T opIndex(size_t col, size_t row) /*const*/ // FIXME Can't be 
const because Chunks.opIndex isn't
         return view[row][col];

void main()
     auto matrix = new Matrix!int(10, 10);
     writeln(matrix[0, 0]);

Oh well, I'll try a different way!

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