[cfe-dev] objc++ enhancements for new c++ features

[James Gregurich via cfe-dev]

> 
> I agree it would be great to get ARC-managed pointers working well in std::shared_ptr and std::weak_ptr.  The usual subtlety with templates is that __strong doesn't show up in C++ mangling, so it's not straightforward to avoid ODR violations when ARC and MRR translation units are linked together.  I think this is solvable, but I doubt it's trivial.


I've come to the conclusion that mixing ARC and non-ARC c++ modules is not viable because of the ODR limitation. Its probably not worth the effort to make it viable. However, all-arc and all-non-arc are both perfectly viable. the use case is the situation where you have a big legacy codebase that will never be made ARC-compatible in its entirety but pieces of it need to work in an ARC process.


the memory header just needs to be changed like so...

template<class _Tp>
class _LIBCPP_TEMPLATE_VIS weak_ptr
{
public:
    typedef _Tp element_type;
private:



#if defined(__OBJC__) && __has_feature(objc_arc)
    element_type __unsafe_unretained * __ptr_;
#else
    element_type*        __ptr_;
#endif

    __shared_weak_count* __cntrl_;


> I'm skeptical of inventing an ObjC++-specific terse lambda syntax.  I'm tempted to let C++ evolve/improve lambda syntax first.

There is no need for any new lambda syntax, and I don't propose any.  the compiler already automatically creates a block from standard lambda syntax in a .mm file...all that works great. What is needed is a directive to tell the compiler to generate a function that will invoke a method with a set of correctly typed arguments. basically...tell the compiler to create a lambda function that does a perfect forwarding to the objc method. once you have that, you can easily stuff a selector invocation inside a std::function or std::packaged_task in the usual manner.


something like this...

std::packaged_task< int (cTest*, NSString*)  >  tmpTask(   @lambda( -[cMyClass methodUsingString:] )   );
auto tmpCFuture = tmpTask.get_future();

auto tmpCPtr = [[[cTest alloc] init] autorelease];

tmpTask( tmpCPtr, @"hello world"  );

auto tmpResult = tmpCFuture.get();




The objc++ compiler works pretty well and is very thorough in integrating the objc world into the c++ world. there are just holes in its capabilities here and there that need to be filled.


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