Throughout last 30 years, numerous head-related transfer function (HRTF) models have been developed and there are more to come. This paper describes a framework based on objective-oriented programming paradigm, in which each HRTF representation method can be implemented as a separate class. Its modular structure allows the source code to be conveniently shared between researchers, while common interface provides easy access to data regardless of the internal structure of the classes. The paper discusses difficulties of designing the framework, maintaining the balance between its flexibility and finding common features of every possible directivity representation. Exemplary use cases are included and explained. Adoption of the framework will enhance possibilities of accuracy comparison between various HRTF models, thus improving the evaluation of current and future representation methods. The framework, developed in the form of a MATLAB toolbox, is designed to handle not only HRTFs but also other types of spatial data, such as e.g. sound source directivity, microphone directivity, etc.