null dereference exception vs. segfault?

[Pelle]

On 08/03/2010 12:32 AM, bearophile wrote:
> Pelle:
>> I think a good thing would be NonNull!T, but I haven't managed to create
>> one. If this structure exists and becomes good practice to use, maybe we
>> can get the good syntax in D3. In 20 years or so :P
>
> Maybe we are talking about two different things, I was talking about nonnull class references/pointers, you seem to talk about nullable values :-) Both can be useful in D, but they are different things.
> Nullable values are simpler to design, they are just wrapper structs that contain a value plus a boolean, plus if you want some syntax sugar to manage them with a shorter syntax.
>
> Bye,
> bearophile

I am talking about non-nullable references indeed. I don't think I 
mentioned nullable types, really.

I also created this, as the simplest NotNull-type concievable:

struct NotNull(T) if(is(typeof(T.init !is null))) {
     private T _instance;

     this(T t) {
         enforce(t !is null, "Cannot create NotNull from null");
         _instance = t;
     }

     T get() {
         assert (_instance !is null,
                 text("Supposed NotNull!(", T.stringof, ") is null"));
         return _instance;
     }
     alias get this;
}


This has the obvious bug in that you can declare a nonnull without an 
initializer and get a null from it. If we ever get @disable this(){} for 
structs, this struct can become better.

I'll probably try it out in some code.