DIP49 - Define qualified postblit

[Kenji Hara]

2013/11/11 Marco Leise <Marco.Leise at gmx.de>

> Am Sun, 10 Nov 2013 21:03:34 +0900
> schrieb Kenji Hara <k.hara.pg at gmail.com>:
>
> > So, separating "inout postblit' and 'unique postblit' may be reasonable.
> >
> > (However, it seems to me that the syntax "this(inout this) inout;" looks
> > weird...
> >
> > Kenji Hara
>
> I see the value in DIP49. There is a hole in the type system
> that needs a proper solution and it is astonishing that the
> "unique" concept is already there in D, but existed under the
> radar of public perception. I haven't read everything, but
> agree with making the language more fail safe any time.
>

Indeed the "unique" concept is not yet enough described in D language
specification. But in recent (past one year or more), it has sometimes been
appeared onto various D features, and I had felt about it while working for
dmd.
The concept had been hidden between D's strong type system (transitive
const and immutability) and 'pure' function long time.


> I just find inout confusing as well. inout as a wildcard for
> const-ness is irritating enough, and with the double meaning
> as unique it might be difficult to read code using inout.
> Are the two concepts really coupled? Does it make the
> implementation of the DIP easier? Or should we have something
> like "unique" as a keyword?


I think rather it is interesting.
Inside inout function, we can treat the inout object as a Schrödinger's cat
(It may be mutable or immutable, or the middle of two == const). And the
necessary requirement to make a copy from an inout object had derived
"unique object" concept. I can agree it looks strange, but there's not any
failures of logic, as far as I know.

Adding a specific keyword for the concept would hurt the language
orthogonality rather.

 Kenji Hara
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