[Issue 8405] Create overload for joiner which is random access for random access ranges

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=8405

--- Comment #5 from bearophile_hugs at eml.cc ---
(In reply to John Colvin from comment #4)

> Unless there is an exploitable pattern in the lengths (rectangular being the
> easiest case), given a NxM range of ranges, it's still O(N).

If you store the row lengths into an array, and you perform a cumulative of
this array, you can perform a binary search on it, to access in O(ln n). At
run-time it can also spot the common case of rectangular matrix, and use a O(1)
code path for that case.


> Perhaps what we need is a generalisation of length for Ranges of Ranges (of
> Ranges ...), called `dimensions` (or `dims`, or `shape`, or whatever seems
> best),

This is Issue 13685 (and it's an easy structure to implement).

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