title: Class _SwiftNativeNSIndexSetBase is implemented in two places
body: <p>I'm somewhat new to Swift programming.  Whenever I run a command line program I set up to play with Swift, it runs fine, but I get the following message in the console.  </p>
  
  <p>Is there a way to resolve the problem, or turn it off?  It repeats so many times that it's hard to see the actual program output in the console with all the noise.  Thanks!</p>
  
  <p>Xcode 8.1</p>
  
  <p><code>objc[1895]: Class _SwiftNativeNSIndexSetBase is implemented in both /Applications/Xcode_8.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx/libswiftCore.dylib (0x100c28668) and /Users/bay/Library/Developer/Xcode/DerivedData/Scratch-amhbiebfsgrxskbcpiinqazhkqpf/Build/Products/Debug/Scratch (0x1003bd540). One of the two will be used. Which one is undefined.</code></p>