Simple immutable example doesn't work - why???

[Dicebot]

On Wednesday, 13 November 2013 at 01:40:27 UTC, Louis Berube 
wrote:
> Does this correctly sum up what I have read? If so, this 
> conversation has cleared up a great deal of my misunderstanding 
> of how "immutable" works. It would be great to see the above 
> examples in a D reference or tutorial (maybe the second edition 
> of Andrei's book?).

Both yes and now. You are correct that those are two observable 
semantics but in practice it is the same immutability. I think it 
becomes easier to get when based on C foundation:

const char * s; // mutable pointer to constant elements"
char * const s; // constant pointer to mutable elements"
const char * const; // constant pointer to constant elements

In C "const" qualifier applies only to part of type it is 
qualified with.

In D, however, both "const" and "immutable" are transitive. That 
means that they do apply to type it is qualified with AND all 
stuff accessible from it. Without explicit brackets those apply 
to whole type:

immutable char * s;  // immutable pointer, immutable elements
immutable(char*) s;  // equivalent to (1)
immutable(char) * s; // mutable pointer, immutable elements

There is no such concept in D type system as "immutable pointer 
to mutable elements". So your two cases both use same 
"immutable", it is just applied to different parts of type.

It is all actually mentioned in TDPL as far as I can remember, 
but maybe relies too much on existing familiarity with 
transitivity concept.