Objective-C++ is a set of standalone header files which can be included in your project to extend the syntax of Objective-CĀ®. Started as a means to reference objects in NSArray containers with a more succinct syntax using the [] operator, the integration of the C++ compiler with Objective-C code is so complete it has grown to include dictionary containers and string concatenation along with regular expression operators and a few utility classes used as a shorthand for common operations.
The header file Foundation++.h contain a number of wrapper classes defining inline functions for certain operators effectively becoming a pre-processor for code. These header files are typically included in your project's "-Prefix.pch" precompiled header file so they are available to all sources in the project. No linking to an external library is required.
An overview is available at this link.