tail const

[Michel Fortin]

On 2010-12-01 09:37:08 -0500, Michel Fortin <michel.fortin at michelf.com> said:

> On 2010-12-01 06:17:24 -0500, Jonathan M Davis <jmdavisProg at gmx.com> said:
> 
>>> I proposed the following a while ago. First allow the class reference
>>> 
>>> to (optionally) be made explicit:
>>> C a;     // mutable reference to mutable class
>>> C ref b; // mutable reference to mutable class
>>> 
>>> And now you can apply tail-const to it:
>>> const(C)ref c;  // mutable reference to const class
>>> const(C ref) d; // const reference to const class
>>> const(C) e;     // const reference to const class
>> 
>> The real issue is not syntax but getting it into the compiler. 
>> Apparently, there
>> are difficulties in implementing tail const in the compiler which made 
>> Walter give
>> up on it in the past. It should be doable, but Walter is totally sick of the
>> issue and doesn't want to put the time in to do it - he has plenty on his plate
>> as it is. So, if it's going to be done, someone else has to step up to 
>> the plate
>> and do it. And with the general lack of dmd developers, that hasn't 
>> happened. No
>> one thus far has had both the inclination and the time.
> 
> Well... I just took a quick look at the problem from inside the 
> compiler. The issue is this: the compiler has a type hierarchy, and 
> TypeClass is one type in it. There is no separate type for a class 
> reference, it just uses TypeClass do designate a class reference, which 
> means that if your TypeClass has the const or immutable modifier, so 
> does your reference. So either we create a TypeClassRef to designate 
> the reference, or we add additional flags to TypeClass for the 
> reference's modifier; in either case many parts of the semantic 
> analysis has to be revised to take this into account.

Turns out it's there's a trick that makes it much simpler than I 
expected. Patch coming soon. ;-)


-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/