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Function std.range.assumeSorted

Assumes r is sorted by predicate pred and returns the corresponding SortedRange!(pred, R) having r as support. To keep the checking costs low, the cost is Ο(1) in release mode (no checks for sorted-ness are performed). In debug mode, a few random elements of r are checked for sorted-ness. The size of the sample is proportional Ο(log(r.length)). That way, checking has no effect on the complexity of subsequent operations specific to sorted ranges (such as binary search). The probability of an arbitrary unsorted range failing the test is very high (however, an almost-sorted range is likely to pass it). To check for sorted-ness at cost Ο(n), use isSorted.

auto auto assumeSorted(alias pred, R) (
  R r
if (isInputRange!(Unqual!R));


import std.algorithm.comparison : equal;

int[] a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
auto p = assumeSorted(a);

assert(equal(p.lowerBound(4), [0, 1, 2, 3]));
assert(equal(p.lowerBound(5), [0, 1, 2, 3, 4]));
assert(equal(p.lowerBound(6), [0, 1, 2, 3, 4, 5]));
assert(equal(p.lowerBound(6.9), [0, 1, 2, 3, 4, 5, 6]));


Andrei Alexandrescu, David Simcha, Jonathan M Davis, and Jack Stouffer. Credit for some of the ideas in building this module goes to Leonardo Maffi.


Boost License 1.0.