This is a nice concrete example of a situation where inheritance is useful for program design. I think i'd go for the "object oriented" approach, but with conv

This is a nice concrete example of a situation where inheritance is useful for program design. I think i'd go for the "object oriented" approach, but with convenience functions to avoid explicit upcasts. Start with three types: cairo_t /* a generic context, could be a page or a pattern */ cairo_page_t cairo_pattern_t Functions only defined on pages take a page: void pdf_page_cmd_bob(cairo_page_t* ctx); Functions defined on both take a generic context: void pdf_ctx_cmd_l(cairo_t* ctx, int x, int y); Then you need some way to upcast from the child types to the parent (which would be implicit in C++ etc): cairo_t* pdf_page_to_ctx(cairo_page_t* ctx); cairo_t* pdf_pattern_to_ctx(cairo_pattern_t* ctx); So a call looks like: pdf_ctx_cmd_l(pdf_page_to_ctx(page), 10, 20); But we can generate this: void pdf_page_cmd_l(cairo_page_t* ctx, int x, int y) { pdf_ctx_cmd_l(pdf_page_to_ctx(ctx), x, y); } Which lets users write this: pdf_page_cmd_l(page, 10, 20); The convenience functions could even be macros. There would be no loss of type safety from using macros that way. There would need to be a lot of convenience functions or macros, but they are trivial, and so could be generated by a script (or another macro!).