Step over the elements of a sequence elements by a specified amount.
This is available through the striding(by:) method on any Sequence.
(0...10).striding(by: 2) // == [0, 2, 4, 6, 8, 10]If the stride is larger than the length of the sequence, the resulting wrapper only contains the first element.
The stride amount must be a positive value.
The striding(by:) method is declared in extension of both Sequence and
Collection:
extension Sequence {
public func striding(by step: Int) -> StridingSequence<Self>
}
extension Collection {
public func striding(by step: Int) -> StridingCollection<Self>
}The reason for this distinction is subtle. The StridingSequence.Iterator type
is unable to skip over multiple elements of the wrapped iterator at once since
that's not part of IteratorProtocol's interface. In order to efficiently
stride over collections that provide a fast way of skipping multiple elements at
once, the StridingCollection type was added which does not provide a custom
Iterator type and therefore always strides over the underlying collection in
the fastest way possible. See the related
GitHub issue for more
information.
A careful thought was given to the composition of these strides by giving a
custom implementation to index(_:offsetBy:limitedBy) which multiplies the
offset by the stride amount.
base.index(i.base, offsetBy: distance * stride, limitedBy: base.endIndex)The following two lines of code are equivalent, including performance:
(0...10).striding(by: 6)
(0...10).striding(by: 2).stride(by: 3)The call to striding(by: k) is always O(1) and access to the next value in
the stride is O(1) if the collection conforms to RandomAccessCollection,
otherwise O(k).
rust has Strided available in a crate.
c++ has std::slice::stride
The semantics of striding described in this documentation are equivalent.