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Function std.range.primitives.popBackExactly

Eagerly advances r itself (not a copy) exactly n times (by calling r.popFront). popFrontExactly takes r by ref, so it mutates the original range. Completes in Ο(1) steps for ranges that support slicing, and have either length or are infinite. Completes in Ο(n) time for all other ranges.

void popBackExactly(Range) (
  ref Range r,
  size_t n
if (isBidirectionalRange!Range);


Unlike popFrontN, popFrontExactly will assume that the range holds at least n elements. This makes popFrontExactly faster than popFrontN, but it also means that if range does not contain at least n elements, it will attempt to call popFront on an empty range, which is undefined behavior. So, only use popFrontExactly when it is guaranteed that range holds at least n elements.

popBackExactly will behave the same but instead removes elements from the back of the (bidirectional) range instead of the front.

See Also

std.range.dropExactly, std.range.dropBackExactly


import std.algorithm.comparison : equal;
import std.algorithm.iteration : filterBidirectional;

auto a = [1, 2, 3];
writeln(a); // [2, 3]
writeln(a); // [2]

string s = "日本語";
writeln(s); // "本語"
writeln(s); // "本"

auto bd = filterBidirectional!"true"([1, 2, 3]);
assert(bd.equal([2, 3]));


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


Boost License 1.0.