the range type
the random access range to find the permutations for.
A forward range of elements of which are an std.range.indexed view into r.
import std.algorithm.comparison : equal; import std.range : iota; assert(equal!equal(iota(3).permutations, [[0, 1, 2], [1, 0, 2], [2, 0, 1], [0, 2, 1], [1, 2, 0], [2, 1, 0]]));
Lazily computes all permutations of r using Heap's algorithm.