Experiment with union/struct field access generation

gen_union.c

// Experiment with expressions for reading from structs and union fields.
// https://godbolt.org/z/G_fsbD

typedef union {
    struct {
        long u;
        short v;
        char w;
    } t1;
    struct {
        int a[2];
        char *p;
    } t2;
} u_type;

#define CONCAT_IMPL(x, y) x##y
#define CONCAT(x, y) CONCAT_IMPL(x, y)
#define GET(Dest, expr)  void CONCAT(get, __COUNTER__)(u_type *up, Dest *dest) { *dest = expr;}

GET(long, up->t1.u)
GET(short, up->t1.v)
GET(char*, &up->t1.w)
GET(int*, up->t2.a)
GET(int, up->t2.a[up->t1.u])
GET(char, *up->t2.p)