struct prefix{
    enum tag{
        t1,
        t2
    } t;
    int some_shared_data;
    int more_shared_data;
}

struct t1{
    prefix p;
    int t1specific;

    @proxy p;
}

struct t2{
    prefix p;
    string t2specific;

    @proxy p;
}

@patternmatching(prefix){
    function t1pattern(prefix* p, t1** out): bool{
        if ( p->t == prefix::tag::t1 ){
            *out = (t1*)p;
            return true;
        }
        return false;
    }

    function t2pattern(prefix* p, t2** out): bool{
        if ( p->t == prefix::tag::t2 ){
            *out = (t2*)p;
            return true;
        }
        return false;
    }
}


void use(prefix* p){
    switch ( p ){
    case t1pattern(concrete):
        // concrete is of type t1*
    case t2pattern(concrete):
        // concrete is of type t2*
    // enforces that you covered all the cases (or requires a default one)
    }
    // unfolds into
    {
        t1* concrete;
        if ( t1pattern(p, &concrete) ){
            // concrete is of type t1*
        }else{
            t2* concrete;
            if ( t2pattern(p, &concrete) ){
                // concrete is of type t2*
            }else{
                unreachable!();
            }
        }
    }
}