protocol BidirectionalIndexType
Inheritance 
Equatable, ForwardIndexType, _Incrementable
View Protocol Hierarchy →


Associated Types 
Distance : _SignedIntegerType = Int
A type that can represent the number of steps between pairs of
Reachability is defined by the ability to produce one value from
the other via zero or more applications of 
Import  import Swift 
Instance Methods
Returns true
if lhs
is equal to rhs
.
Equality implies substitutability. When x == y
, x
and
y
are interchangeable in any code that only depends on their
values.
Class instance identity as distinguished by tripleequals ===
is notably not part of an instance's value. Exposing other
nonvalue aspects of Equatable
types is discouraged, and any
that are exposed should be explicitly pointed out in
documentation.
Equality is an equivalence relation
x == x
istrue
x == y
impliesy == x
x == y
andy == z
impliesx == z
Inequality is the inverse of equality, i.e. !(x == y)
iff
x != y
.
Declaration
func ==(lhs: Self, rhs: Self) > Bool
Declared In
Equatable
Returns the result of advancing self
by n
positions.
Returns:
 If n > 0
, the result of applying successor
to self
n
times.
 If n < 0
, the result of applying predecessor
to self
n
times.
 Otherwise, self
.
Requires: n >= 0
if only conforming to ForwardIndexType
Complexity:
 O(1) if conforming to RandomAccessIndexType
 O(abs(n)
) otherwise
Declaration
func advancedBy(n: Self.Distance) > Self
Declared In
ForwardIndexType
Returns the result of advancing self
by n
positions, or until it
equals limit
.
Returns:
 If n > 0
, the result of applying successor
to self
n
times
but not past limit
.
 If n < 0
, the result of applying predecessor
to self
n
times
but not past limit
.
 Otherwise, self
.
Requires: n >= 0
if only conforming to ForwardIndexType
.
Complexity:
 O(1) if conforming to RandomAccessIndexType
 O(abs(n)
) otherwise
Declaration
func advancedBy(n: Self.Distance, limit: Self) > Self
Declared In
ForwardIndexType
Measure the distance between self
and end
.
Requires:
 start
and end
are part of the same sequence when conforming to
RandomAccessSequenceType
.
 end
is reachable from self
by incrementation otherwise.
Complexity:
 O(1) if conforming to RandomAccessIndexType
 O(n
) otherwise, where n
is the function's result.
Declaration
func distanceTo(end: Self) > Self.Distance
Declared In
ForwardIndexType
Returns the previous consecutive value in a discrete sequence.
If self
has a welldefined successor,
self.successor().predecessor() == self
. If self
has a
welldefined predecessor, self.predecessor().successor() ==
self
.
Requires: self
has a welldefined predecessor.
Declaration
func predecessor() > Self
Returns the next consecutive value in a discrete sequence of
Self
values.
Requires: self
has a welldefined successor.
Declaration
func successor() > Self
Declared In
_Incrementable
Default Implementations
Declaration
func advancedBy(n: Self.Distance) > Self
Declared In
BidirectionalIndexType
, ForwardIndexType
Declaration
func advancedBy(n: Self.Distance, limit: Self) > Self
Declared In
BidirectionalIndexType
, ForwardIndexType
Measure the distance between self
and end
.
Requires:
 start
and end
are part of the same sequence when conforming to
RandomAccessSequenceType
.
 end
is reachable from self
by incrementation otherwise.
Complexity:
 O(1) if conforming to RandomAccessIndexType
 O(n
) otherwise, where n
is the function's result.
Declaration
func distanceTo(end: Self) > Self.Distance
Declared In
ForwardIndexType
Where Self : ReverseIndexType
Returns the previous consecutive value before self
.
Requires: The previous value is representable.
Declaration
func predecessor() > Self
Returns the next consecutive value after self
.
Requires: The next value is representable.
Declaration
func successor() > Self
An index that can step backwards via application of its
predecessor()
method.