Returns a sequence formed from repeated lazy applications of next to a mutable state.
SDK
- Xcode 8.0+
Framework
- Swift Standard Library
Declaration
func sequence<T, State>(state: State, next: @escaping (inout State) -> T?) -> UnfoldParameters
stateThe initial state that will be passed to the closure.
nextA closure that accepts an
inoutstate and returns the next element of the sequence.
Return Value
A sequence that yields each successive value from next.
Discussion
The elements of the sequence are obtained by invoking next with a mutable state. The same state is passed to all invocations of next, so subsequent calls will see any mutations made by previous calls. The sequence ends when next returns nil. If next never returns nil, the sequence is infinite.
This function can be used to replace many instances of Any that wrap a closure.
Example:
// Interleave two sequences that yield the same element type
sequence(state: (false, seq1.makeIterator(), seq2.makeIterator()), next: { iters in
iters.0 = !iters.0
return iters.0 ? iters.1.next() : iters.2.next()
})