FunctionSwift

stride(from:to:by:)

Returns a sequence from a starting value to, but not including, an end value, stepping by the specified amount.

func stride<T>(from start: T, to end: T, by stride: T.Stride) -> StrideTo<T> where T : Strideable

Parameters

start: The starting value to use for the sequence. If the sequence contains any values, the first one is start.
end: An end value to limit the sequence. end is never an element of the resulting sequence.
stride: The amount to step by with each iteration. A positive stride iterates upward; a negative stride iterates downward.

Returns

A sequence from start toward, but not including, end. Each value in the sequence steps by stride.

Overview

You can use this function to stride over values of any type that conforms to the Strideable protocol, such as integers or floating-point types. Starting with start, each successive value of the sequence adds stride until the next value would be equal to or beyond end.

for radians in stride(from: 0.0, to: .pi * 2, by: .pi / 2) {
    let degrees = Int(radians * 180 / .pi)
    print("Degrees: \(degrees), radians: \(radians)")
}
// Degrees: 0, radians: 0.0
// Degrees: 90, radians: 1.5707963267949
// Degrees: 180, radians: 3.14159265358979
// Degrees: 270, radians: 4.71238898038469

You can use stride(from:to:by:) to create a sequence that strides upward or downward. Pass a negative value as stride to create a sequence from a higher start to a lower end:

for countdown in stride(from: 3, to: 0, by: -1) {
    print("\(countdown)...")
}
// 3...
// 2...
// 1...

If you pass a value as stride that moves away from end, the sequence contains no values.

for x in stride(from: 0, to: 10, by: -1) {
    print(x)
}
// Nothing is printed.