C++ to Objective-C accessor

example.mm

#import "MyObject.h"

//--- pass by reference ---
  MyObject *obj = [[MyObject alloc] init];
  ...
  auto *cppObject = new MyObjectCpp(obj);
  cppObject->SayHello("Hello!");
//---
...

//-- Create an instance of MyObject from cpp code ...
  auto *cppObject = new MyObjectCpp();
  cppObject->SayHello("Hello!");
//--
  

Info.txt

based on: "A shortcut for wrapping Objective-C objects in C++"
          http://philjordan.eu/article/mixing-objective-c-c++-and-objective-c++  

don't forget to turn off ARC:

  You can disable ARC for individual files in XCode under the 'Build Phases' tab in the build target's properties.
  Fold out the 'Compile Sources' section and add `-fno-objc-arc` to the compiler flags for the file(s) in question.
  
  for MyObject.mm (`-fno-objc-arc`)
  
  |- example.mm  (Usage example)
  |
  |- MyObject.h  (Objective-C header)
  |- MyObject.mm (Objective-C + CPP part implementation)
  |- MyObjectCpp.h (C++ header)
  

MyObject.h

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface MyObject : NSObject

-(void)sayHello:(NSString *)string;

@end

NS_ASSUME_NONNULL_END

MyObject.mm

#import "MyObject.h"

#include "MyObjectCpp.h"
#include <string>

namespace abc {

    MyObjectCpp::MyObjectCpp() : wrapped([[MyObject alloc] init]){

    }
    MyObjectCpp::MyObjectCpp(MyObject *obj):wrapped(obj) {

    }
    MyObjectCpp::~MyObjectCpp() {
        [wrapped release];
    }

    void MyObjectCpp::SayHello(const std::string &text){
        [wrapped sayHello:[NSString stringWithUTF8String:text.c_str()]];
    }
}


@implementation MyObject

-(void)sayHello:(NSString *)string {

    NSLog([NSString stringWithFormat:@"Say: %@", string]);
}

@end

MyObjectCpp.h

#ifndef MyObjectCpp_h
#define MyObjectCpp_h

#include <string>
#import <objc/runtime.h>

#ifdef __OBJC__
#import "MyObject.h"

@class MyObject;
#else
typedef struct objc_object MyObject;
#endif

namespace abc {

    class MyObjectCpp {
        MyObject *wrapped;
    public:
        MyObjectCpp();
        MyObjectCpp(MyObject *obj);
        ~MyObjectCpp();
        void SayHello(const std::string &text);
    };
}

#endif /* MyObjectCpp_h */