Flattening an integer type

I did the following in order to convert an Integer type to an array of smaller (or same size) integer types:

extension FixedWidthInteger {
    public func flattened<T: FixedWidthInteger>() -> [T] {
        let selfSize = MemoryLayout<Self>.size
        let resultSize = MemoryLayout<T>.size
        precondition(selfSize >= resultSize,
                     "Size of result (\(T.self): \(resultSize)) must not be greater than size of field (\(Self.self): \(selfSize))")
        return (0 ..< selfSize / resultSize).map {
            T(truncatingIfNeeded: self >> Self($0 * T.bitWidth))

let ui32: UInt32 = 0x12345678
let fourBytes: [UInt8] = ui32.flattened()
print(fourBytes.map { String($0, radix: 16) }) // ["78", "56", "34", "12"]

Does something like this already exist, and I just can't find it?

Also, it seems to also work as well as an extension to BinaryInteger. Any good reason to choose one over the other?

Is there a better name? Names can be hard!