How to manually deprecate members

You can use the Available tag, for example :

@available(*, deprecated)
func myFunc() { 
    // ...
}

Where * is the platform (iOS, iOSApplicationExtension, macOS, watchOS, tvOS, * for all, etc.).

You can also specify the version of the platform from which it was introduced, deprecated, obsoleted, renamed, and a message :

@available(iOS, deprecated:6.0)
func myFunc() { 
    // calling this function is deprecated on iOS6+
}

Or

@available(iOS, deprecated: 6.0, obsoleted: 7.0, message: "Because !")
func myFunc() {
    // deprecated from iOS6, and obsoleted after iOS7, the message "Because !" is displayed in XCode warnings
}

If your project targets multiple platforms, you can use several tags like so :

@available(tvOS, deprecated:9.0.1)
@available(iOS, deprecated:9.1)
@available(macOS, unavailable, message: "Unavailable on macOS")
func myFunc() {
    // ...
}

More details in the Swift documentation.

Starting Swift 3 and Swift 4, the version number is optional. You can now simply type:

@available(*, deprecated)
func foo() {
    // ...
}

Or if you want a message go along with it:

@available(*, deprecated, message: "no longer available ...")
func foo() {
    // ...
}