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

[Joseph Rushton Wakeling]

On 18/12/13 21:11, ilya-stromberg wrote:
> Sorry if I miss something, but I don't understand this analogy.
>
> `const` means that original type can be `mutable` or `immutable`, so both
> `mutable` and `immutable` types can be implicitly converted to the `const` type.
>
> If I understand DIP correctly, unique postblit/constructor returns `unique` type
> that can be implicitly converted to the all of `mutable`, `immutable` and
> `const` types. So, this behavior is the opposite of current `const` behavior.
>
> So, where is analogy here?

Well, as far as I understand it (happy to be corrected if wrong), the point of 
this DIP is to offer a way to _easily_ create immutable and const instances of 
objects (which as I recall from the last time I tried to do it, is a real PITA).

So, you have your regular mutable constructor -- 'this' with no qualifications 
-- which can be used to construct mutable instances.

You have this(...) immutable, which can be used to construct immutable instances.

And you have this(...) const (aka "unique"), which can be used to construct both 
immutable and mutable instances.

It seems to me that this is a very natural relation to the existing 
interpretation of mutable, immutable and const variables by the language, and 
e.g. the way that immutable, mutable and const function parameters are addressed.