> exposing struct definitions in header files

Hiding the struct like:

    typedef struct foo_t foo_t;
    /* ... */
    foo_t *foo_new();

kinda forces heap allocs. There are times when you want to allocate on the stack, and not use alloca.

Most of the time, I still keep struct definitions in header files, but API wise I always write functions or macros for anything that touches them and discourage direct access to struct members. Depending on the use case of course. Abstract types have their uses too.