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I just learned about the __bridge cast today and I am not understanding the implications behind it:

Why would Apple create Two frameworks that are so close to one another that they are toll-free interchangeable.

What benefit does one gain by using one framework over the other?

Are there any good tutorials out there that show strategies to use when bridging between the two frameworks?

Cœur
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user3689657
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2 Answers2

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Some years ago, you had the choice to program code in Apple environment either in C or in Objective-C. From basic low-level to graphic application on the Mac, you'd had access to both API.

Both API needed the same abstractions and concepts to not deny developers that would use C or Objective-C. As Objective-C is a superset of C, it was easy to embed one C structure in a Objective-C class. This avoid to recreate a different abstraction and make the interaction between both easier.

The benefits of C version, is that you are working at a lower layer that make your code technically lighter and faster as you don't need to use the Objective-C runtime. I said technically because it is lower level than Objective-C, but I'm not sure you can grab the difference today in current application. The benefit of Objective-C version is dynamicity and object oriented code. You could do OO with the C version, but it would be more verbose.

The best documentation for bridging is the LLVM arc documentation: http://clang.llvm.org/docs/AutomaticReferenceCounting.html

Mike ash has a very good explanation on toll free bridging here: https://mikeash.com/pyblog/friday-qa-2010-01-22-toll-free-bridging-internals.html

yageek
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If I'm not mistaken, Core Foundation uses object orientation (and hence resides on a bit higher level of abstraction) whereas Foundation does not. In practice this means that one uses Objective C whereas the other uses C. This is a reoccurring pattern in Apple's system software. In principle you can use either framework of mix them both: __bridge__ helps you by allowing the use of foreign entities as if they were legit Objective-C objects of a certain class.

Drux
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