Why would you want to avoid using a struct? Add a macro that declares the appropriate struct and get at least a tiny bit of type checking.

With some clever use of _Generic you could even build specialised functions for that type and get pretty good type checking

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;

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

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