Making RCSlice and DIP74 work with const and immutable

[Zach the Mystic via Digitalmars-d]

On Sunday, 1 March 2015 at 16:45:04 UTC, Zach the Mystic wrote:
> On Sunday, 1 March 2015 at 01:40:40 UTC, Andrei Alexandrescu 
> wrote:
>> One possible solution is to add a "@mutable" or "@metadata" 
>> attribute similar to C++'s keyword "mutable". Walter and I 
>> both dislike that solution because it's hamfisted and leaves 
>> too much opportunity for abuse - people can essentially create 
>> unbounded amounts of mutable payload for an object claimed to 
>> be immutable. That makes it impossible (or unsafe) to optimize 
>> code based on algebraic assumptions.
>
> I need to get educated on this issue. First suggestion: Just 
> break the type system by encouraging the idiom of using casts 
> in opAddRef and opRelease. It's too easy, but I don't know why.

Well I guess it's about optimizing code. So the question is what 
the optimizer needs to know, and why.