[dmd-internals] Questions: how consttructors and postblits work with qualifiers

[Jonathan M Davis]

On Wednesday, May 09, 2012 18:10:29 kenji hara wrote:
> Question 4:
>     Qualified postblits should work?
> 
>         struct S {
>             this(this) {}
>             this(this) immutable {}
>         }
>         S sm;
>         const S sc = sm;     // runs this(this)? or runs only blit copy? [X]
> immutable S si = sm; // runs this(this)immutable?
> 
>     But, with current dmd, multiple postblits conflicts each other.
>     Even if should do, I can't imagine how they works in some cases, like

Qualified postblits make no sense, given that if the object is const or 
immutable, you _can't_ alter it without violating the type system. But without 
them, you can't copy const or immutable objects which require a postblit. 
Walter and Andrei have stated in the past that they had a plan for solving 
this, but AFAIK, they've never actually revealed what it is. My best guess 
would be to introduce copy constructors for const and immutable objects, but I 
don't know. Regardless, this is a situation that definitely needs to be 
clarified and properly sorted out.

- Jonathan M Davis