Null references (oh no, not again!)

[BCS]

Hello Christopher,

> BCS wrote:
> 
>> Hello Walter,
>> 
>>> Andrei suggests making a library type work for this rather than a
>>> language attribute, but it's still an extra thing that will have to
>>> be specified everywhere where used.
>>> 
>> I've considered trying to make a template that compile time enforces
>> Non-null usage but can, with a version flag, be switched to a simple
>> alias/typedef of the internal type. Near zero overhead and possibly
>> just as strong a guard.
>> 
> It's impossible.
> 
> You can create a struct that will throw an exception if you use it
> uninitialized, or if you try assigning null to it. But the struct
> cannot require that it is initialized.
> 
> You can add a contract that requires the struct be initialized, and
> put the contract and declaration in a template.
> 

Your right, but if you switch to a class and factory with no public constructor, 
you can make it work. The problem of perf going down the drain is avoidable 
if you can (in that mode) enforce compile time checking of most cases and 
requiter calls to do run time checks for the rest. If the template works 
right, than flipping back to alias/typedef mode leaves the run time checks 
and leave the unchecked code as correct while doing away with the perf problems.