Example code for http://juliankniephoff.wordpress.com/2011/03/27/use-objective-c-classes-in-cpp-opaquely-readably-and-safely

CMakeLists.txt

CMAKE_MINIMUM_REQUIRED(
	VERSION
	2.8
)

PROJECT(
	speech
)

FIND_LIBRARY(
	APPKIT_LIBRARY
	AppKit
)
FIND_PATH(
	APPKIT_INCLUDE_DIR
	AppKit/AppKit.h
)
INCLUDE_DIRECTORIES(
	${APPKIT_INCLUDE_DIR}
)

INCLUDE_DIRECTORIES(
	.
)

ADD_LIBRARY(
	speech
	speaker_impl.mm
	speaker.mm
)
TARGET_LINK_LIBRARIES(
	speech
	${APPKIT_LIBRARY}
)
SET_TARGET_PROPERTIES(
	speech
	PROPERTIES
	COMPILE_FLAGS -fobjc-arc
)

ADD_EXECUTABLE(
	speak
	speak.cpp
)
TARGET_LINK_LIBRARIES(
	speak
	speech
)

speak.cpp

#include <speaker.hpp>

int main(int argc, char *argv[])
{
	your::friends::library::speech::speaker speaker;
	for (int word = 1; word < argc; ++word)
	{
		speaker.speak(
			argv[word]
		);
		while (
			speaker.is_speaking()
		);
	}
}

speaker.hpp

#ifndef YOUR_FRIENDS_LIBRARY_SPEECH_SPEAKER_HPP
#define YOUR_FRIENDS_LIBRARY_SPEECH_SPEAKER_HPP

#include <speaker_impl_fwd.hpp>
#include <string>

namespace your
{
namespace friends
{
namespace library
{
namespace speech
{

class speaker
{
public:
	speaker();
	~speaker();

	void
	speak(
		std::string const &
	);

	bool
	is_speaking() const;

private:
	speaker_impl * const pimpl_;
};

}
}
}
}

#endif

speaker.mm

#include <speaker.hpp>
#include <speaker_impl.hpp>
#include <Foundation/NSString.h>

your::friends::library::speech::speaker::speaker():
	pimpl_(
		new your::friends::library::speech::speaker_impl
	)
{
}

your::friends::library::speech::speaker::~speaker()
{
	delete pimpl_;
}

void
your::friends::library::speech::speaker::speak(
	std::string const & string
)
{
	[pimpl_->synth_ startSpeakingString:
		[NSString stringWithUTF8String:
			string.c_str()
		]
	];
}

bool
your::friends::library::speech::speaker::is_speaking() const
{
	return [pimpl_->synth_ isSpeaking];
}

speaker_impl.hpp

#ifndef YOUR_FRIENDS_LIBRARY_SPEECH_SPEAKER_IMPL_HPP
#define YOUR_FRIENDS_LIBRARY_SPEECH_SPEAKER_IMPL_HPP

#import <AppKit/NSSpeechSynthesizer.h>

namespace your
{
namespace friends
{
namespace library
{
namespace speech
{

struct speaker_impl
{
public:
	speaker_impl();

	NSSpeechSynthesizer * const synth_;
};

}
}
}
}

#endif

speaker_impl.mm

#include <speaker_impl.hpp>

your::friends::library::speech::speaker_impl::speaker_impl():
	synth_(
		[[NSSpeechSynthesizer alloc] init]
	)
{
}

speaker_impl_fwd.hpp

#ifndef YOUR_FRIENDS_LIBRARY_SPEECH_SPEAKER_IMPL_FWD_HPP
#define YOUR_FRIENDS_LIBRARY_SPEECH_SPEAKER_IMPL_FWD_HPP

namespace your
{
namespace friends
{
namespace library
{
namespace speech
{

struct speaker_impl;

}
}
}
}

#endif