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

[Timon Gehr]

On 05/20/2013 01:39 AM, Andrei Alexandrescu wrote:
> On 5/19/13 7:06 PM, deadalnix wrote:
>> On Sunday, 19 May 2013 at 22:32:58 UTC, Andrei Alexandrescu wrote:
>>> How was there a bug if everything was properly synchronized? You
>>> either describe the matter with sufficient detail, or acknowledge the
>>> destruction of your anecdote. This is going nowhere.
>>>
>>
>> I explained over and over. A field is initialized to null, while the
>> object lock is owned, and later to its value, while it is locked. In the
>> meantime, another thread access the object, owning the lock, assuming
>> the field is always initialized.
>
> How does another thread thread accesses the object "owning the lock"
> when the assignment occurs under lock?
>

lock{ initialize to null. }
lock{ in the meantime assume correctly initialized. }
lock{ initialize correctly. }

This is nothing new. I think he has been pretty clear about what the 
issue is from the beginning.

> How would non-null fix this? Would the object have type Maybe?
>

This is one possibility. In this case, the type system would have 
prevented the null dereference.
In the other case, the type system would have caught the invalid 
initialization.