1. 8.0.1
    InitializerSwiftBSONSwift

    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.

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

    Parameters

    source

    An integer to convert to this type.

    Overview

    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