In C23 this approach is nice, but in older versions of C we end up with awful macros where we need to define the structure before we use it.

    #define Array(T) struct array_##T
    #define DEFINE_ARRAY(T) struct array_##T { size_t len; T *elems; }
    
    DEFINE_ARRAY(int);
    Array(int) foo;
    Array(int) bar;

C23 has relaxed rules for redefining the same struct, so we can avoid having to create the struct up front.

    #define Array(T) struct array_##T { size_t len; T *elems; }

    Array(int) foo;
    Array(int) bar;