Struct with default ctor (Was: [dmd-beta] dmd 2.064 beta take 2)

[deadalnix]

On Sunday, 19 May 2013 at 01:20:31 UTC, Walter Bright wrote:
> I understand that. But the rationale you gave for having a 
> default constructor was to be able to disable default 
> construction.
>

RAII or construction based on template parameters.

> I know that some languages have a special syntax for non-null 
> pointers. I disliked this solution for D because non-nullable 
> pointers are just one instance of creating a type with a 
> limited set of values. Why not go for a general solution? Why 
> not create a mechanism where a type can be defined that can 
> only consist of prime numbers, for example? Why not ranged 
> integer types?

Actually most languages does the reverse. They have non nullable 
type, and provide Nullable/Option/Maybe/whatever to allow for 
nullable type. It allow to ensure that null don't pops up in 
unexpected places, and that null must be handled when it is an 
option.

The current solution is to rely on faith, and I remember someone 
talking about that at DConf recently.

Now that what other languages does is cleared, let's do some 
consideration on null.

A pointer point on something. For instance, an int* point on an 
integer. null doesn't point on a integer. Non nullable pointer 
aren't a restricted set of values, as, by definition, null isn't 
a value that point to an int. That doesn't stand either.

D already have thing like Nullable in the standard lib. 
Introducing Maybe is also pretty easy. Adding NonNullable in 
addition to Nullable sound like something is not quite right.

The benefit we get from null, ie having a default initialization 
for everything, is moot if @disable this() is introduced, so it 
is questionable at this point how useful it really is except as 
make up over current implementation deficiencies.

Finally it has to be added that null cause holes in @safe in ways 
that are difficult to impossible to solve.