Hi!

I thought that this should compile:
class Foo{}

const(Foo) foo = new Foo;// the same that const Foo foo?
foo = new Foo;

but compiler say that foo is const reference and it can't modify it.
It is normally?If yes,how can I declare non-const reference to const instance of class?

On Wednesday, October 10, 2012 19:02:31 Zhenya wrote:
> Hi!
> 
> I thought that this should compile:
> class Foo{}
> 
> const(Foo) foo = new Foo;// the same that const Foo foo?
> foo = new Foo;
> 
> but compiler say that foo is const reference and it can't modify
> it.
> It is normally?If yes,how can I declare non-const reference to
> const instance of class?

const Foo and const(Foo) are the same thing. They both create a const reference to const data. This is in contrast to a pointer where const Bar* and const(Bar)* are different. With a reference, there is no way to indicate that the object is const but not the reference. The type system just doesn't support the idea of a class object existing separately from a reference, so there's no way to make that distinction.

If you want to have a mutable reference to a const object, then you need a wrapper around the reference where the wrapper is mutable but the reference isn't. std.typecons.Rebindable does this. It's what you should use.

- Jonathan M Davis

On Wednesday, 10 October 2012 at 17:35:48 UTC, Jonathan M Davis wrote:
> On Wednesday, October 10, 2012 19:02:31 Zhenya wrote:
>> Hi!
>> 
>> I thought that this should compile:
>> class Foo{}
>> 
>> const(Foo) foo = new Foo;// the same that const Foo foo?
>> foo = new Foo;
>> 
>> but compiler say that foo is const reference and it can't modify
>> it.
>> It is normally?If yes,how can I declare non-const reference to
>> const instance of class?
>
> const Foo and const(Foo) are the same thing. They both create a const
> reference to const data. This is in contrast to a pointer where const Bar* and
> const(Bar)* are different. With a reference, there is no way to indicate that
> the object is const but not the reference. The type system just doesn't
> support the idea of a class object existing separately from a reference, so
> there's no way to make that distinction.
>
> If you want to have a mutable reference to a const object, then you need a
> wrapper around the reference where the wrapper is mutable but the reference
> isn't. std.typecons.Rebindable does this. It's what you should use.
>
> - Jonathan M Davis

Thank you)