Generic Initializer

init(truncatingIfNeeded:)

Creates a new instance from the bit pattern of the given instance by truncating or sign-extending if needed to fit this type.

Declaration

convenience init<T>(truncatingIfNeeded source: T) where T : BinaryInteger

Parameters

source

An integer to convert to this type.

Discussion

When the bit width of T (the type of source) is equal to or greater than this type’s bit width, the result is the truncated least-significant bits of source. For example, when converting a 16-bit value to an 8-bit type, only the lower 8 bits of source are used.

let p: Int16 = -500
// 'p' has a binary representation of 11111110_00001100
let q = Int8(truncatingIfNeeded: p)
// q == 12
// 'q' has a binary representation of 00001100

When the bit width of T is less than this type’s bit width, the result is sign-extended to fill the remaining bits. That is, if source is negative, the result is padded with ones; otherwise, the result is padded with zeros.

let u: Int8 = 21
// 'u' has a binary representation of 00010101
let v = Int16(truncatingIfNeeded: u)
// v == 21
// 'v' has a binary representation of 00000000_00010101

let w: Int8 = -21
// 'w' has a binary representation of 11101011
let x = Int16(truncatingIfNeeded: w)
// x == -21
// 'x' has a binary representation of 11111111_11101011
let y = UInt16(truncatingIfNeeded: w)
// y == 65515
// 'y' has a binary representation of 11111111_11101011

See Also

Converting Integers

init<T>(T)

Creates a new instance from the given integer.

init?<T>(exactly: T)

Creates a new instance from the given integer, if it can be represented exactly.

init<Other>(clamping: Other)

Creates a new instance with the representable value that’s closest to the given integer.

init(bitPattern: UInt)

Creates a new instance with the same memory representation as the given value.