Er, you answered a question about const with an answer about immutable. :\
My point is, what in the world does transitive const have to do with
transitive immutable?
Can't you have immutable(T) be transitive while const(T) being "normal",
as in C/C++? If not, why not?
On 9/22/2011 10:36 AM, Peter Alexander wrote:
On 21/09/11 6:15 PM, Mehrdad wrote:
I can't find the thread, but I remember someone (bearophile?) mentioned
that the reason we have transitive const is to support purity.
I don't think I understand why this is necessary, though -- could
someone please explain why we have transitive const, and what problems
it fixes?
Thanks!
It's mostly for concurrent programming.
If I pass an immutable(T) reference type to another thread then I need
to be guaranteed that the object is entirely immutable.
If it weren't for transitive const/immutable, this would be possible:
class Foo
{
Foo m_ref;
this() { m_ref = this; }
Foo get() immutable { return m_ref; }
}
immutable(Foo) foo = new Foo();
Foo surprise = foo.get(); // un-immutable-ified!
