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version 2.109.1

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Function std.range.primitives.popFrontN

popFrontN eagerly advances r itself (not a copy) up to n times (by calling r.popFront). popFrontN takes r by ref, so it mutates the original range. Completes in Ο(1) steps for ranges that support slicing and have length. Completes in Ο(n) time for all other ranges.

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

popBackN behaves the same as popFrontN but instead removes elements from the back of the (bidirectional) range instead of the front.

Returns

How much r was actually advanced, which may be less than n if r did not have at least n elements.

See Also

std.range.drop, std.range.dropBack

Example

int[] a = [ 1, 2, 3, 4, 5 ];
a.popFrontN(2);
writeln(a); // [3, 4, 5]
a.popFrontN(7);
writeln(a); // []

Example

import std.algorithm.comparison : equal;
import std.range : iota;
auto LL = iota(1L, 7L);
auto r = popFrontN(LL, 2);
assert(equal(LL, [3L, 4L, 5L, 6L]));
writeln(r); // 2

Example

int[] a = [ 1, 2, 3, 4, 5 ];
a.popBackN(2);
writeln(a); // [1, 2, 3]
a.popBackN(7);
writeln(a); // []

Example

import std.algorithm.comparison : equal;
import std.range : iota;
auto LL = iota(1L, 7L);
auto r = popBackN(LL, 2);
assert(equal(LL, [1L, 2L, 3L, 4L]));
writeln(r); // 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.