https://issues.dlang.org/show_bug.cgi?id=18280

          Issue ID: 18280
           Summary: std.algorithm.comparison.cmp for non-strings should
                    call opCmp only once per item pair
           Product: D
           Version: D2
          Hardware: All
               URL: http://dlang.org/
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P3
         Component: phobos
          Assignee: nobody@puremagic.com
          Reporter: n8sh.secondary@hotmail.com

Right now when comparing non-string ranges std.algorithm.comparison.cmp calls the comparison predicate twice for every pair of elements to determine their order. When the elements have overloaded `opCmp` and the predicate is "a < b" we only need to call `opCmp` once for each pair.

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