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

[Simen Kjaeraas]

On Sun, 19 May 2013 20:23:21 +0200, Walter Bright  
<newshound2 at digitalmars.com> wrote:

> On 5/19/2013 5:02 AM, Simen Kjaeraas wrote:
>>> By definition? Pointer semantics are what we choose it to mean.
>> Of course. But which definition is saner:
>
> For many types, it is extremely useful to have some sort of "invalid"  
> value for it. null fills that role nicely for pointers, just as nan does  
> for floating point types, and 0xFF does for UTF-8.
>
> There's not anything insane about it. The Nullable type constructor even  
> exists in order to provide such an invalid state for types (like int)  
> which normally do not have one.
>
> Yes, I do understand there's a role for pointers which cannot hold the  
> invalid value.

I contend that not only is there a role for them, but that most pointers
should never be null. Here's two questions that convinced me:

1. How many functions that take a pointer or class reference make sense
    to call with null in that pointer/reference?

2. If pointers were non-nullable by default, how often would you need to
    reach for the nullable one?

I argued in another post that nullable by default is analogous to using a
string instead of an int - any number representable in an int is
representable in a string, *and* the string can represent error states.
But if you only want valid ints, there's no reason to use a string.

-- 
Simen