According to http://dlang.org/const3.html
The simplest immutable declarations use it as a storage class. It can be used to declare manifest constants.
So, immutable string s = "..."; should be a manifest constant.
If it is a constant that it can be used in switch(...).
switch(someStr)
{
case s: ...; // Error: case must be a string or an integral
constant, not s.
}, but string s = "..."; works good. Why?
