What's the deal with "Warning: explicit element-wise assignment..."

[via Digitalmars-d]

On Wednesday, 30 April 2014 at 11:52:14 UTC, Dicebot wrote:
> And that would have been quite a close guess actually as 
> walkLength is constrained to accept only finite InputRanges :) 
> "walk" here implies iteration and iteration implies O(n).

The common term is "count", "countNodes", "countElements" etc... 
Why all the specialized functions in algorithm.d? Why not just 
have a default predicate that is always true and do compile time 
optimizations? I find fragmented libraries hard to use.