Why D const is annoying

[SomeDude]

On Wednesday, 2 May 2012 at 06:44:30 UTC, Mehrdad wrote:
> Whether the compiler makes **GUARANTEES** about code is 
> _irrelevant_ to whether or not the language uses 'const' to 
> improve performance.
>
> You could very well have a language which **enforces** 
> const-ness (i.e. doesn't prevent casting it away), but which 
> _doesn't_ use it to improve performance.
> Or which does.
>

Yes, pure functional languages do provide this kind of guarantee, 
by simply forbidding immutability at the cost of copying objects. 
I agree D's solution isn't "pure" as it must allow mutability, 
and I suspect it can't be, unless it starts copying objects all 
over the place. That means that when you use the immutable 
keyword, you *really* mean it and you *must* think that way. If 
you want to mutate your object, you have to copy it to another 
object. Thats how strings are designed. For me, your example 
doesn't prove that the tool is broken, it proves that you don't 
know how to use immutability. It's really another paradigm, which 
has its uses, in particular in concurrent programming.