Is Swift incompatible with pre-ARC Objective-C?

Question

I'm starting to add Swift files to a very large, legacy Objective-C project that doesn't use ARC.

When I compile the project, I get warnings for every property emitted in the ProjectName-Swift.h bridge header:

• No 'assign', 'retain', or 'copy' attribute is specified - 'assign' is assumed
• Default property attribute 'assign' not appropriate for non-GC object

It seems like Swift is emitting ARC-based Objective-C code.

Is this a limitation/bug in this particular release of Swift, or is Swift designed to work only with ARC code?

Answer 1

You can mix ARC and non-ARC code. All ARC-compiled code does is manage its memory automatically to the user. You should enable ARC for your project and then disable ARC for individual files using -fno-objc-arc or enable ARC for just Swift files using -fobjc-arc (this may not be necessary as the compiler may automatically be adding it). Swift code is eventually compiled to use the same Objective C runtime, and ARC calls inserted by the compiler are the same as in Objective C. After compilation, ARC and non-ARC code behave the same.