Function std.algorithm.mutation.bringToFront

bringToFront takes two ranges front and back, which may be of different types. Considering the concatenation of front and back one unified range, bringToFront rotates that unified range such that all elements in back are brought to the beginning of the unified range. The relative ordering of elements in front and back, respectively, remains unchanged.

Performs Ο(max(front.length, back.length)) evaluations of swap.

Prototype

size_t bringToFront(Range1, Range2)(
  Range1 front,
  Range2 back
)
if (isInputRange!Range1 && isForwardRange!Range2);

Preconditions

Either front and back are disjoint, or back is reachable from front and front is not reachable from back.

Returns

The number of elements brought to the front, i.e., the length of back.

See Also

STL's rotate

Example

The simplest use of bringToFront is for rotating elements in a buffer. For example:

auto arr = [4, 5, 6, 7, 1, 2, 3];
auto p = bringToFront(arr[0 .. 4], arr[4 .. $]);
assert(p == arr.length - 4);
assert(arr == [ 1, 2, 3, 4, 5, 6, 7 ]);

Example

The front range may actually "step over" the back range. This is very useful with forward ranges that cannot compute comfortably right-bounded subranges like arr[0 .. 4] above. In the example below, r2 is a right subrange of r1.

import std.algorithm.comparison : equal;
import std.container : SList;

auto list = SList!(int)(4, 5, 6, 7, 1, 2, 3);
auto r1 = list[];
auto r2 = list[]; popFrontN(r2, 4);
assert(equal(r2, [ 1, 2, 3 ]));
bringToFront(r1, r2);
assert(equal(list[], [ 1, 2, 3, 4, 5, 6, 7 ]));

Example

Elements can be swapped across ranges of different types:

import std.algorithm.comparison : equal;
import std.container : SList;

auto list = SList!(int)(4, 5, 6, 7);
auto vec = [ 1, 2, 3 ];
bringToFront(list[], vec);
assert(equal(list[], [ 1, 2, 3, 4 ]));
assert(equal(vec, [ 5, 6, 7 ]));