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digitalmars.D.learn - shifted lowerBound with ranges

Hi, I am trying to convert some pointer based C++ code to ranges.

Given a sorted list of numbers w and a value v, I want to extract 
a sublist containing
exactly s numbers <=v and all numbers >v.

The following code "works", but it is ugly:
-the result of shiftedLowerBound is not a slice of the original 
array and it has a different type
-if the operation is repeated with increasing v the search 
algorithm cannot use the result of the previous computation.

I looked at the code of std.range and it seems that the result 
can be achieved by using the function getTransitionIndex of 
SortedRange, but it is private. Am I overlooking something that 
makes it possible to achieve my goal using the range interface?


import std.stdio;
import std.range;
import std.algorithm;

auto shiftedLowerBound(W,V)(W w, V v, long s )
     auto ws=assumeSorted(w);
     auto pps=ws.trisect(v);
     long k=pps[1].length-s;
     return chain( (pps[0])[$+min(k,0)..$], (pps[1])[max(k,0)..$], 
pps[2] );

void main()
     long[] vs=[10,15];
     int s=6;
Jun 23 2019