-rewrite-objc and Objective-C in clang

Question

Recently, I have one problem. The clang can translate Objective-C to c++ use -rewrite-objc. So I think, the first step. clang compile Objective-C to C++. And then compile only can use c++ compiler. Is it do like this? clang first translate Objective-C to C++ with runTime, and then compile to the machine code?

Emmi

Answer 1

-rewrite-objc exists to translate ObjC to C++ so it can be compiled in the Visual Studio. It is still Objective-C semantics and you still need the objective-c runtime. It is not magically converting Objective-C to the C++ OO architecture.

This is much more like when Objective-C was implemented as a pre-compiler extension.

It all relies on the fact that Objective-C classes are just C structures with fancy behavior and objective-c method calls all can be translated to calls to objc_msgSend().

Enameling

Thank you. But I also what to know, dose Clang translate OC to machine code directly instead of to C++ first when compiling? – Brickle

It translates it to C++ code (mostly C, really) before compilation; specifically, before the visual studio compiler takes over, typically. – Enameling

sorry for disturb you. In this question, the top answer confuse me. So dose any C/C++ IR live when compiling OC? – Brickle

@Brickle Totally different situation; that question is talking about compiling code to IR. This question is referring to the ObjC rewriter. The goal of the rewriter is to spit straight C/C++ code that can be compiled by another compiler -- typically the Visual C++ compiler in Visual Studio. – Enameling