Constant relationships between non-constant objects

[Justin Whear via Digitalmars-d]

On Wed, 18 Jun 2014 01:31:32 +0000, Sebastian Unger wrote:

> Hi there,
> 
> I'm an experient C++ developer and am trying to switch to / learn D.
> What I've seen so far is mostly quite straight forward and VERY nice.
> 
> There's only one catch so far for me for which Googling has only found
> the discouraging answer of: It can't be done in D.
> 
> I have two classes A and B. Each object of class A is associated with a
> particular object of class B. This association is not supposed to change
> throughout the lifetime of the object of A.
> 
> How am I supposed to express this in D, given that D's const is too
> strong for this? I don't need any guarantees from the const that can be
> used for thread safety or parallelisation. All I need is the compiler
> not letting me change the reference to the B object inside the A object.
> 
> Does D have some way of expressing this?
> 
> Or has D really done away with the MOST important use case of const
> (preventing developer mistakes! Not optimization.)
> 
> Cheers,
> Seb

I think you may be mixing up const and immutable.  What do you mean about 
const being too strong?

It seems that does what you want:

class A
{
    const B bff;

    this(B bestBuddy)
    {
        bff = bestBuddy;
    }
}