Unnamed Structure and Union Fields

In ISO C11, it's legal and useful to define a struct like

struct {
    int a;
    union {
        int b;
        float c;
    };
    int d;
} foo;

in such a case, an instance foo of struct bar would have foo.b and foo.c accessing the same memory as different types. In addition, it is also legal and useful to do this:

struct foo {
    int a;
};

struct bar {
    struct foo;
    float b;
    char *c;
};

in which case, a pointer to bar can be easily and safely cast to a pointer to foo, and an instance baz of struct bar would have member baz.a as an int.

Millfork already supports both structure and union types, and I feel that this ability would make it even better.