Possible way to achieve lazy loading with const objects

[Regan Heath]

On Mon, 26 Sep 2011 13:01:29 +0100, Steven Schveighoffer  
<schveiguy at yahoo.com> wrote:
> On Sat, 24 Sep 2011 00:11:52 -0400, Jonathan M Davis
>> 6.  If the S being constructed is shared or immutable and __varProp is  
>> not
>> called in the constructor, then __varProp is called immediately after  
>> the
>> constructor (or at the end of the constructor if that works better for  
>> the
>> compiler).
>
> Why?  What if the calculation is very expensive, and you never access  
> var?
>
> Besides, we can already pro-actively initialize data in an immutable  
> constructor, what is the benefit here?

I think this is to avoid threading issues, like double checked locking  
problems etc.

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