In Objective-C it was sometimes useful to use static string constants to define alternate API keys (for example to differentiate between RELEASE and DEBUG keys for analytics packages, like MixPanel, Flurry or Crashlytics):
#if DEBUG
static NSString *const API_KEY = @"KEY_A";
#else
static NSString *const API_KEY = @"KEY_B";
#endif
and then...
[Analytics startSession:API_KEY];
How does this translate to Swift, since the Swift compiler no longer uses a preprocessor?
Apple included full support for Swift preprocessor flags as of Xcode 8, so it's no longer necessary to set these values in "Other Swift Flags".
The new setting is called "Active Compilation Conditions", which provides top-level support for the Swift equivalent of preprocessor flags. You use it in exactly the same way as you would "Other Swift Flags", except there's no need to prepend the value with a "-D" (so it's just a little cleaner).
From the Xcode 8 release notes:
Active Compilation Conditionsis a new build setting for passing conditional compilation flags to the Swift compiler. Each element of the value of this setting passes to swiftc prefixed with-D, in the same way that elements ofPreprocessor Macrospass to clang with the same prefix. (22457329)
You use the above setting like so:
#if DEBUG
let accessToken = "DebugAccessToken"
#else
let accessToken = "ProductionAccessToken"
#endif
=1... I lost a bit of time trying to figure out why it wasn't working when I did. So, I thought I'd share this tidbit to help the next fellow. :] Anyways, thanks for your answer here!
DEBUG in Active Compilation Conditions and DEBUG=1 in Preprocessor Macros and this configuration does not work at all. Should i remove DEBUG=1 ?? Not clear from the above comments.Build Configuration first. Check this answer stackoverflow.com/questions/9063100/… for more info.UPDATED: Xcode 8 now supports this automatically, see @dwlz's response above.
Prior to Xcode 8, you could still use Macros in the same way:
#if DEBUG
let apiKey = "KEY_A"
#else
let apiKey = "KEY_B"
#endif
However in order for them to be picked up by Swift, you need to set "Other Swift Flags" in your target's Build Settings:
-D flag
-D prefixIn swift packages you have to do this inside of the swiftSettings argument to .target in your Package.swift file. Use the define method (Apple documentation) or Swift documentation
targets: [
.target(name: String,
dependencies: [Target.Dependency],
path: String?,
exclude: [String]?,
sources: [String]?,,
cSettings: [CSetting]?,
cxxSettings: [CXXSetting]?,
swiftSettings: [SwiftSetting]?,
linkerSettings: [LinkerSetting]?),
Mine looks like this and it works!
swiftSettings: [
.define("VAPOR")
]
in my code I can conditionally compile using this:
#if VAPOR
swiftSettings for each of my targets.As a follow up observation, try not to keep api keys / secrets in plaintext in the repository. Use a secrets management system to load the keys / secrets into the user's environment variables. Otherwise step 1 is necessary, if acceptable.
../set_keys.sh that contains a list of export API_KEY_A='<plaintext_key_aef94c5l6>' (use single quote to prevent evaluation)source ../set_keys.sh and move it to the top of execution orderAPI_KEY_A="$API_KEY_A" That captures the environment variable into the compiler define which is later used in each clang invocation for each source file.
Example directory structure
[10:33:15] ~/code/memo yes? tree -L 2 .
.
├── Memo
│ ├── Memo
│ ├── Memo.xcodeproj
│ ├── Memo.xcworkspace
│ ├── Podfile
│ ├── Podfile.lock
│ └── Pods
└── keys