Ranges and backward iteration

[Era Scarecrow]

On Sunday, 29 July 2012 at 23:26:09 UTC, Andrew wrote:
> I have a use case where I would like to be able to pass both a
> forward and backward iteration of an array to a function:
>
> void foo(InputR, OutputR)(InputR i, OutputR j)
>    if (isInputRange!InputR && isOutputRange!(OutputR, InputR))
> {
> ...
> }
>
> main()
> {
>     //forward:
>     foo(a[1..n], b[1..n]);
>     //backward:
>     foo(retro(a[n..$]), retro(b[n..$]));
>
>     //do stuff with b as it has been constructed now...
> }
>
> This doesn't work (retro doesn't appear to return a Range, but
> rather an object of type "Result", which I don't understand), 
> but
> the intent should be clear.
>
> How do I do this? What am I missing?  There doesn't seem to be a
> "backward iterator" equivalent in std.range.



  isBidirectionalRange perhaps?

[quote]
Returns true if R is a bidirectional range. A bidirectional range 
is a forward range that also offers the primitives back and 
popBack. The following code should compile for any bidirectional 
range.
[/quote]