What guarantees does D 'const' provide, compared to C++?

[Mehrdad]

> I remember being told many times that D's 'const' provides 
> stronger guarantees than C++'s 'const'.


I also remember being told that the compiler considers it UB to 
cast away const-ness in references, unlike in C++, which gives 
you more guarantees.

But I'm having trouble coming up with a pieces of source code 
that illustrate the issue.