mysql-native ResultRange + map

[Steven Schveighoffer via Digitalmars-d-learn]

On 7/5/17 12:04 PM, crimaniak wrote:
> Hi all!
> 
> After some hard time with debugging, I found ResultRange returned by 
> query() and Prepared::query() of mysql-native package can't be combined 
> with map() because after map() it becomes empty resultset.
> 
[snip]
> As you see simple each() and foreach() works, but all examples with 
> map() involved always empty. Can anybody explain such strange behavior?
> 

Because of the temporary copy likely inside map closes the connection.

See the bug I reported: https://github.com/mysql-d/mysql-native/issues/117

I work around this in my code by moving the temporary copy. But I'm 
sorry to say you likely will not be able to fix map.

I think Nick's comment is interesting, "Seems that using struct dtors 
without refcounting should in general be regarded as a code smell?"

It's a good question. I've also always added ref counting when wanting 
to "auto close" a struct's resources. In fact, I can't really think of a 
good use of destructors for structs that isn't for reference counting 
itself.

-Steve