x.RC.__postblit () is not callable using argument types () const

[Dan]

On Tuesday, 5 February 2013 at 15:06:47 UTC, Maxim Fomin wrote:
> The root of the problem is in:
>
> struct DAssociativeArray(Key, Value)
> {
>     struct Slot
>     {
>         Value value;
>     }
> }
>
> struct RC {
>   this(this) {  }
> }
>
> void main()
> {
>     DAssociativeArray!(int, const(RC)) goo;
> }
>
> which doesn't compile (this is how Value[Key] is rewritten).
>

I see - thanks. I assume it should compile and without the 
postblit it does. So - the original code is fine and there is a D 
problem with associative arrays.

- Wouldn't the scenario be exactly the same without 
ValuationHistory? That is, if I comment out the member 
_valuationHistory, the goo member is not changed in structure at 
all, and yet it compiles just fine.
- Does this mean that "no one" or "very few" developers store 
structs with postblits as value types in the standard associative 
array? Maybe I just do things differently than others.

The way I see it you have to choose how you want to develop your 
structs/classes. I have chosen to use structs and templates and 
avoid classes, thinking this would greatly simplify things. Any 
struct needs to establish up front whether it will have value 
semantics or reference semantics. So far, I have preferred value 
semantics as data sharing leads to confusion. So if I have arrays 
in a struct I include postblits to provide value semantics. In 
another thread Walter made clear his distaste for postblits and 
preference for reference semantics coupled with copy on write 
semantics where needed. That approach, just does not seem worth 
it without more systematic support for COW. Assuming postblits 
are the issue, I don't understand why they are so hard to get 
right.

Thanks
Dan