What’s new in Swift 4.2.1?

Yes! There appears to be such a thing, and it was silently shipped alongside Xcode 10’s first point-release, 10.1. Contrary to major releases, Swift 4.2.1’s release wasn’t accompanied by a blog post, nor was its entry added to the Swift changelog. Is there a reason for this all this mystery, or is the 4.2.1 really just so insignificant?

Pierpaolo Frasa must’ve been wondering the same thing, based on his recent post on the Swift forums:

My mac wants me to upgrade to Xcode 10.1, which will include Swift 4.2.1.
However, I can’t find any mention of that swift version either on the download page or in the changelog.

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The list of resolved issues is rather short, with 8 compiler issues fixed, and just one problem resolved in the standard library. The highlights include: 

  • A fix for ambiguous compilation error messages like “Command CompileSwiftSources failed with a nonzero exit code”
  • The Bundle class’s init(for:) initializer now works consistently with Swift classes, not just Objective-C classes
  • Long file paths containing white space no longer cause build failures
  • A mutating method that returns Self on a value of protocol type can now successfully be invoked

Check out the “Swift Compiler” and “Swift Standard Library” sections in the Xcode release notes for a complete list of the changes, complete with code samples.

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