OBJCXX

About

OBJCXX is a C++ wrapper library for the Objective-C language and the Apple's Foundation framework.

It allows you to use the complete Foundation framework using C++ on macOS and Windows without the need of an Objective-C compiler.

Technical Details

This library uses the Objective-C runtime to interact with the Foundation framework's classes.
As the Objective-C runtime is a C API, an Objective-C compiler is not required.

All Foundation classes are wrapped by C++ counterparts, which can be used with automatic allocation.
Memory is automatically managed. Objective-C instances are retained by their C++ counterparts, and released when necessary.

Example

Here's an hello world example using OBJCXX:

#include <OBJCXX.h>

int main()
{
    NS::Log( "%@", NS::String( "hello, world" ) );
    
    return 0;
}

Here's a more complex example:

#include <OBJCXX.h>

int main()
{
    /* Equivalent to @autoreleasepool */
    NS::AutoreleasePool ap;
    
    /* NSMutableArray */
    {
        NS::MutableArray o;
        
        std::cout << o << std::endl;
        
        o.addObject( NS::String( "hello, world" ) );
        o.addObject( NS::String( "hello, universe" ) );
        
        std::cout << o << std::endl;
    }
    
    /* NSMutableDictionary */
    {
        NS::MutableDictionary o;
        
        std::cout << o << std::endl;
        
        o.setObjectForKey( NS::String( "hello, world" ),    NS::String( "key-1" ) );
        o.setObjectForKey( NS::String( "hello, universe" ), NS::String( "key-2" ) );
        
        std::cout << o << std::endl;
    }
    
    /* NSFileManager */
    {
        NS::Error e;
        
        std::cout << NS::FileManager::defaultManager().attributesOfItemAtPath( "/~/Desktop/", e ) << std::endl;
    }
    
    return 0;
}

Creating Objective-C classes from C++

OBJCXX also allows you to dynamically create Objective-C classes at runtime.
While this is of course possible using the Objective-C runtime, OBJCXX makes this process much more simpler.

As an example:

#include <OBJCXX.h>

int main()
{
    /* Class Foo inheriting from NSObject */
    OBJCXX::ClassBuilder cls( "Foo", "NSObject" );
    
    /* Adds properties - Getters and setters are automatically generated */
    cls.addProperty( "title",     OBJCXX::ClassBuilder::TypeObject );
    cls.addProperty( "isEnabled", OBJCXX::ClassBuilder::TypeBool );
    cls.addProperty( "index",     OBJCXX::ClassBuilder::TypeSignedInt );
    
    /* Registers the class so it can be used */
    cls.registerClass();
    
    return 0;
}

The above example creates and registers a fully working Objective-C class similar to:

@interface Foo: NSObject

@property( nonatomic, readwrite, strong ) id   title;
@property( nonatomic, readwrite, assign ) BOOL isEnabled;
@property( nonatomic, readwrite, assign ) int  index;

@end

Adding custom methods

The example above only adds properties to the class, but custom methods can be added as well, and bound to C++ methods.

Imagine the following C++/Objective-C wrapper class, inheriting directly from NS::Object:

class Foo: public NS::Object
{
    public:
        
        OBJCXX_USING_BASE( Bar, Object )
        
        Foo(): Object( "Foo" )
        {}
        
        NS::String test( int x )
        {
            return std::to_string( x );
        }
};

The Objective-C class can be created the following way:

{
    OBJCXX::ClassBuilder cls( "Foo", "NSObject" );
    
    cls.instanceMethod< Foo, NS::String, int >( "test", &Foo::test, "" ).add< id, int >();
    cls.registerClass();
}

The template parameters of instanceMethod are the expected C++ types, while the template parameters of add are the expected Objective-C type.
This is necessary in order to convert the objects to/from C++ and Objective-C.

If the types are the same, the template parameters of add can be omitted, as they will be deduced automatically.

The example above will effectively add a instance method to the Foo class, which will be callable either from Objective-C or from C++, meaning the following:

objc_msgSend( Foo(), "test", 42 );

will effectively ends up calling the C++ method implementation.

License

OBJCXX is released under the terms of the MIT license.

Repository Infos

Owner:			Jean-David Gadina - XS-Labs
Web:			www.xs-labs.com
Blog:			www.noxeos.com
Twitter:		@macmade
GitHub:			github.com/macmade
LinkedIn:		ch.linkedin.com/in/macmade/
StackOverflow:	stackoverflow.com/users/182676/macmade