Very limited shared promotion

[Ola Fosheim Grostad]

On Tuesday, 18 June 2019 at 09:01:47 UTC, Manu wrote:
> The access function returns a scoped lock object with a ref 
> count. You may take many read ref's, a write access has a 
> maximum of 1 ref. You may not take a read and a write lock at 
> the same time.

But, you could take the address of an attribute or object and 
retain it?  So this is only by convention? Or is the type system 
able to ensure this?