DIP53 and DIP49 (ver2) - New definitions for qualified constructors and postblits

[Timon Gehr]

On 12/18/2013 04:42 AM, Kenji Hara wrote:
> http://wiki.dlang.org/DIP53
> Redesign currently implemented qualified constructor concept.
> ...

Roughly speaking, this DIP just removes a language feature and changes 
the syntax of another feature to something less descriptive. I think 
implementing this is a net loss.

> http://wiki.dlang.org/DIP49
> Improved points from version 1:
> - Swap meanings of 'this(this) inout' and 'this(this) const'
> - Inout postblit now covers all cheap (== not rebind indirections)
> copies between same qualifiers
>
> Kenji Hara

What about just mentioning the qualifiers of source and target of the 
copy explicitly?

this(this){ ... } // mutable source, mutable target
this(immutable this){ ... } // immutable source mutable target
this(const this)immutable{ ... } // const source, immutable target
this(const this)const{ ... } // const source, const target
// ...
this(inout this)inout{ ... } // source and target have the same qualifier
// ...
this(this)inout{ ... } // mutable source, arbitrary target
// ...
this(const this)inout{ ... } // const source, arbitrary target

Whenever source and target are (potentially) incompatible, the postblit 
ensures that all fields with incompatible types in source and target are 
reinitialized.

Only unique expressions convert to 'inout' anyway, hence the last 
signature above would correspond to unique postblit in the current proposal.

This would be more explicit, strictly more expressive and require less 
special casing in the compiler implementation.