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

[Andrei Alexandrescu]

On 5/19/13 8:46 PM, Steven Schveighoffer wrote:
> I just wanted to chime in with this understanding of the bug that I am
> reading from deadalnix's descriptions:
>
> SomeObj obj;
> shareTheObj(&obj); // goes to other threads
> obj = new SomeObj; // initialize obj
>
> This is likely simpler than the actual problem, but I think this is the
> gist of it.
>
> A Non-Nullable solution WOULD solve the race:
>
> SomeObj obj; // Compiler: nope, can't do that, must initialize it.
>
> Now, with an "invalid state" not available like null, is the developer
> more likely to go through the trouble of building an invalid state for
> obj, in order to keep the racy behavior? No. He's just going to move the
> initialization:
>
> SomeObj obj = new SomeObj;
> shareTheObj(&obj);
>
> In essence the point of the anecdote is that a Non-Nullable reference
> would have PROMOTED avoiding the race condition -- it would have been
> harder to keep the racy behavior.

One can only assume the entire point was to delay initialization of the 
object to its first use/sharing point, so the changed pattern simply 
initializes the object eagerly, thus missing the benefits of the 
pattern. Otherwise that's an instance of the old adage "initialize 
variables at the point of definition". That, granted, non-null 
references do help with.


Andrei