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version 2.110.0

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Function std.range.primitives.popFrontExactly

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 popFrontExactly(Range)(
  ref Range r,
  size_t n
)
if (isInputRange!Range);

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.

See Also

std.range.dropExactly, std.range.dropBackExactly

Example

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

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

string s = "日本語";
s.popFrontExactly(1);
writeln(s); // "本語"
s.popBackExactly(1);
writeln(s); // "本"

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

Authors

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

License

Boost License 1.0.