[ruby-core:100472] [Ruby master Feature#17277] Make Enumerator#with_index yield row and col indices for Matrix

Issue #17277 has been updated by marcandre (Marc-Andre Lafortune).


What about chained enumerators?

```ruby
matrix.each(:diagonal).each_const(2).with_index do |elem, ?|
```

It's not clear to me how that could be implemented efficiently, do you have an idea?

Finally, what is the use case?

I would rather add `map_with_index`....

----------------------------------------
Feature #17277: Make Enumerator#with_index yield row and col indices for Matrix
https://bugs.ruby-lang.org/issues/17277#change-88091

* Author: greggzst (Grzegorz Jakubiak)
* Status: Open
* Priority: Normal
----------------------------------------
Currently this code seems to be counting index based on the internal array of arrays and it's not correct for the matrix which should return row and col indices

```
Matrix[[0,2,3,4], [6,7,8,9], [1,4,5,8]].each.with_index { |e, index| print "#{index} " } ; puts
0 1 2 3 4 5 6 7 8 9 10 11 
=> nil
```

I'm aware of the fact that you could do following and you get the correct results:

```
Matrix[[0,2,3,4], [6,7,8,9], [1,4,5,8]].each_with_index { |e, row, col| print "[#{row}, #{col}] " } ; puts
[0, 0] [0, 1] [0, 2] [0, 3] [1, 0] [1, 1] [1, 2] [1, 3] [2, 0] [2, 1] [2, 2] [2, 3] 
=> nil
```

You can even chain `each_with_index` with other enumerators and access indices within them e.g.
```
Matrix[[0,2,3,4], [6,7,8,9], [1,4,5,8]].each_with_index.filter_map { |e, row, col| [row, col] if e % 4 == 0}
=> [[0, 0], [0, 3], [1, 2], [2, 1], [2, 3]]
```

However, I feel we should override `with_index` for Matrix so it returns row and col indices.



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