Check the Version of System Swift in a Swift Program

swiftVersion.swift

/* Copyright (c) 2020 Michael Chen.
   Licensed under Apache 2.0        */

func swiftVersionMajor () -> UInt {
#if swift(>=5.0)
    return 5
#elseif swift(>=4.0)
    return 4
#elseif swift(>=3.0)
    return 3
#elseif swift(>=2.0)
    return 2
#else
    return 1
#endif
}

func swiftVersionMinor () -> UInt {
#if swift(>=5.3)
    return 3
#elseif swift(>=5.2)
    return 2
#elseif swift(>=5.1)
    return 1
#elseif swift(>=5.0)
    return 0
#elseif swift(>=4.2)
    return 2
#elseif swift(>=4.1)
    return 1
#elseif swift(>=4.0)
    return 0
#elseif swift(>=3.2)
    return 2
#elseif swift(>=3.1)
    return 1
#elseif swift(>=3.0)
    return 0
#elseif swift(>=2.2)
    return 2
#elseif swift(>=2.1)
    return 1
#elseif swift(>=2.0)
    return 0
#elseif swift(>=1.2)
    return 2
#elseif swift(>=1.1)
    return 1
#elseif swift(>=1.0)
    return 0
#endif
}

print("Swift version: \(swiftVersionMajor()).\(swiftVersionMinor())")