howto-feature-flag.md

Feature flags

Environment flags

One way to setup a feature flag or toggle is to create an environment variable

And then call it like this

var url: String = {

        if ProcessInfo.processInfo.environment["MOCK_API"] == "YES" {
            return "http://localhost:8000/orderDetails/"
        }

        return "https://prod/orderDetails"
}()

Environment variable only work on the simulator and locally connected devices. To create a feature flag that will work into production we need a compile time flag.

Compile time flags

Compile time flags are setup up in configuration files (xcconfig) or as a Swift Compiler - Custom Flag.

Swift Compiler - Custom Flag

Target > Build Settings then search for 'Swift Compiler - Custom'.

Here you set a flag on the Active Compilation Condition for each of your targets by double clicking the row (i.e. Debug) and where is says <Multiple Values> you add your new flag (i.e. FOO).

You can then access the flag at runtime like this

func isFeatureAvailable() -> Bool {
    #if FOO
        return false
    #else
        return true
    #endif
}

Note: In older versions of Xcode and projects you will still see the old Other Swift Flags section. Where here you add a compile time flag per line. Also, these properties often are read in from configuration files (.xcconfig).

And then still access the same way

#if MOCK_API
    return URL(string: "https://mock")
#else
    return URL(string: "https://prod")
#endif

Links that help

• Conditional Compilation Block - Swift
• Sundell Feature Flags in Swift