Conditional Imports in Swift - swift

Question

I have a Log function I use in various apps. Its convenient for this to also make Crashlytics logging calls since I use it throughout the app.
However, not every app uses Crashlytics. In Objective C you could handle this with preprocessor conditions.
How would one handle this in code? I think there are ways to make the function conditional perhaps. But how would I optionally or weak import Crashlytics?
import Foundation
//import Crashlytics
/// Debug Log: Log useful information while automatically hiding after release.
func DLog<T>(message: T, filename: String = __FILE__, function: String = __FUNCTION__, line: Int = __LINE__) {
// CLSLogv("\(NSString(string: filename).lastPathComponent).\(function) line \(line) $ \(message)", getVaList([]))
print("[\(NSString(string: filename).lastPathComponent) \(function) L\(line)] \(message)")
}

Answer 1

You can do this now in Swift 4.1 with the new canImport() directive. This is the Swift Evolution proposal that describes how it works: https://github.com/apple/swift-evolution/blob/master/proposals/0075-import-test.md
So you could do:
#if canImport(Crashlytics)
func dLog() {
// use Crashlytics symbols
}
#endif

Answer 2

I would do it a different way in Swift. I would make my log function extensible. I would have an array of log closures that do actual logging and my dlog function would invoke all of them e.g.
private var logFunctions: [(String) -> ()] = [ { print($0) } ]
func dlog(message: String, filename: String = __FILE__, function: String = __FUNCTION__, line: Int = __LINE__)
{
let logMessage = "[\(NSString(string: filename).lastPathComponent) \(function) L\(line)] \(message)"
for log in logFunctions
{
log(logMessage)
}
}
dlog("Hi", filename: "file", function: "function", line: 1)
print("---")
logFunctions.append{ print("New print: " + $0) }
dlog("Hi", filename: "file", function: "function", line: 2)
Output is
[file function L1] Hi
---
[file function L2] Hi
New print: [file function L2] Hi
So in any application that supports Crashlytics, in your application start up code, you add the crashlytics logger to your array of loggers i.e.
import Crashlytics // Only needed in the Swift file with app start up code
// ...
logFunctions.append{ CLSLogv($0, getVaList([])) }
Of course you should encapsulate all of the above in a class or something.

Answer 3

This is possible in Swift even though the Swift compiler does not include a preprocessor.
import Foundation
#ifdef DEBUG
import Crashlytics
#endif
/// Debug Log: Log useful information while automatically hiding after release.
func DLog<T>(message: T, filename: String = __FILE__, function: String = __FUNCTION__, line: Int = __LINE__) {
#ifdef DEBUG
CLSLogv("\(NSString(string: filename).lastPathComponent).\(function) line \(line) $ \(message)", getVaList([]))
#else
print("[\(NSString(string: filename).lastPathComponent) \(function) L\(line)] \(message)")
#endif
}
Now, the following code is untested and MAY need some tweaking - but it can help if you want to clean up your code! #transparent will inline the body of the code, by the way.
import Foundation
#ifdef DEBUG
import Crashlytics
#transparent printfn(item: String) {
CLSLogv(item, getVaList([])
}
#else
let printfn = println
#endif
/// Debug Log: Log useful information while automatically hiding after release.
func DLog<T>(message: T, filename: String = __FILE__, function: String = __FUNCTION__, line: Int = __LINE__) {
printfn("\(NSString(string: filename).lastPathComponent).\(function) line \(line) $ \(message)")
}
Please note: you must set the "DEBUG" symbol as it is not predefined. Set it in the "Swift compiler - Custom Flags" section of the compiler, "Other Swift Flags" line. You cand efine the DEBUG symbol with the -D DEBUG entry.
Hope I was able to help!