## ForwardIndexType

protocol ForwardIndexType

Represents a discrete value in a series, where a value's successor, if any, is reachable by applying the value's successor() method.

Inheritance Equatable, _Incrementable View Protocol Hierarchy → Distance : _SignedIntegerType = Int A type that can represent the number of steps between pairs of Self values where one value is reachable from the other. Reachability is defined by the ability to produce one value from the other via zero or more applications of successor. import Swift

### Instance Methods

func ==(_:rhs:) Required

Return 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 triple-equals === is notably not part of an instance's value. Exposing other non-value 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 is true
• x == y implies y == x
• x == y and y == z implies x == z

Inequality is the inverse of equality, i.e. !(x == y) iff x != y.

#### Declaration

func ==(lhs: Self, rhs: Self) -> Bool

#### Declared In

Equatable

Return 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

Return 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
func distanceTo(_:)

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
func successor() Required

Return the next consecutive value in a discrete sequence of Self values.

Requires: self has a well-defined successor.

#### Declaration

func successor() -> Self

_Incrementable