import std.algorithm.comparison : equal; import std.algorithm.iteration : filterBidirectional; auto a = [1, 2, 3]; a.popFrontExactly(1); assert(a == [2, 3]); a.popBackExactly(1); assert(a == [2]); string s = "日本語"; s.popFrontExactly(1); assert(s == "本語"); s.popBackExactly(1); assert(s == "本"); auto bd = filterBidirectional!"true"([1, 2, 3]); bd.popFrontExactly(1); assert(bd.equal([2, 3])); bd.popBackExactly(1); assert(bd.equal([2]));
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 O(1) steps for ranges that support slicing, and have either length or are infinite. Completes in O(n) time for all other ranges.
Note: 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.