snej / swiftier

Quick-and-dirty Objective-C to Swift translator

What It Is

— A quick and dirty script that reads Objective-C source code and outputs a rough, partial translation to Swift. Expect a similar level of fluency and elegance as produced by Google Translate, i.e. not much.

— A tool to save you from a whole lot of annoying search-and-replace grunt-work when converting Objective-C code to Swift.

What It Isn't

— A pushbutton converter like Xcode's "Modernize Syntax" tool that outputs compilable code. Not even!

— Anything resembling a sane parser. (I've written parsers and I know the difference.) Mais non! this is a nasty soup of regular expressions. It's ugly and limited, but hey, I got it running in a few hours.

— Complete. No way! This is a one-day hack, and there are a lot of things it could do that it doesn't yet, or that it could do better. If I'm motivated (or if you are!) then maybe someday it'll do those things.

What It Converts

• #import <Foo/Foo.h> —> import Foo
• Class or category interfaces (@interface through @end) are stripped. (TBD: Use them to determine which methods are public and which correspond to properties.)
• @implementation Foo ... @end —> class Foo { ... }
• Instance variable declarations (in braces right after @implementation) turn into private vars.
• Method header lines e.g. - (BOOL) foo:(int)bar {...} —> func foo(bar :Int) -> Bool { ... }
• init methods are treated specially to accord with Swift's initializer rules:
  • If the method name starts with initWith... then the rest of the name turns into the keyword of the first parameter.
  • The self = [super init] boilerplate turns into an initializer call to super or self.
  • The if (self) boilerplate check is stripped out.
  • The return self at the end is stripped out.
• Local variable declarations. Those initialized with a value are defined using let, those with no value are var.
• Many common type names when used in method headers or variable declarations; like NSUInteger —> UInt and NSString —> String.
• A few common constants, like YES —> true and NO —> false.
• A few common functions, like NSLog —> println and NSAssert —> assert.
• @"..." —> "..."
• Message-send expressions in square brackets. (Limitation: Only if they fit on a single line. Those broken across multiple lines are currently left alone. Sorry!)
• Trailing semicolons — removed!
• Parentheses around if conditions — removed!
• Braces around single-statement if bodies — added!

Q: "Dude, you forgot _____. wtf! It should totally convert those too."
A: "We're so glad you've decided to help! Pull requests welcome ^_^"

How To Use It

Just download the file swiftier.rb, make sure its executable bit is set, and feed it the contents of a .m file either by path or by stdin. The output will be written to stdout. For example:

$ swiftier.rb FlappyCapybara.m >FlappyCapybara.swift

or to inspect what all your code would look like:

$ cat *.m | swiftier.rb | mate

License

I'm putting this in the public domain, or if you will, under the Thelemaic License: Do what thou wilt shall be the whole of the law. Have fun :)