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Comment by aidenn0 | Hacker News Reader

> As an example, let's say you use ZII and allocate 100 objects in a single allocation

If you want to do that you can always use a nullable type. You can always assign it to a non-nullable type after initialization if you plan on using the aggregate a lot.

Usually you provide a vector type though, which has an underlying nullable array, but maintains a fill-index such that for all i < fill-index it the value is initialized, and then you have two indexing operations; one which returns a nullable type and the other which bounds-checks and returns a non-nullable type.

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This could make sense for a from-scratch language, but C3 is trying to be an evolution of C, and such constraints would make it so much of a different language that it would be way out of scope.

I think Rust and similar languages fill that niche already, so there is no real need to try to offer that type of alternative.

I think we are miscommunicating. Let's imagine a language called "C@" where the only difference is that "@" is used in place of "*" for a non-nullable pointer type:

  typedef struct {
     foo @*data; //Non-nullable pointer to nullable pointer of foo
     size_t size;
     size_t fill;
  } foo_vec;
  
  void foo_vec_push(foo_vec @v, foo @x) {
    if (v->fill == v->size) {
      //realloc and zero data
    } else {
      data[idx++] = v;
    }
  }
  
  foo @ foo_vec_get(foo_vec @v, size_t idx) {
    if (idx < fill) {
      return (foo @)(data+idx);
    } else {
      abort();
    }
  }

I'm not sure how this constraint makes it "so much of a different language" at all.

In this case, how would you prevent the user from seeing an invalid foo_vec before initialization? This is either "oh, it's in an illegal state", in which case it's just an annotation without deeper enforcement or you need to somehow enforce that a non-null pointer is never seen, am I not right?

1. It's not quite trivial to statically disallow use-before-initialization, but it's definitely a solved problem if you disallow returning uninitialized variables.

2. The other option is to disallow declaration without initialization of non-nullable values. If you can't declare an uninitialized foo_vec, then the user can't ever see an invalid foo_vec.

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