I don't know why but I feel myself confused with struct variables
in D. As far as structs are value types this means that they are
copied everywhere except when passing from/to functions with ref
qualifier.
So what I don't understand is when each of these methods for
struct variables are called (postblit/opAssign/constructors). Am
I right that postblit is used to assign to struct another value
with the same type? But what is used when I assign value of the
same type, but with another qualifier (const to mutable,
immutable to mutable). Should I overload opAssign instead? Or
create special constructor to make new value of type that I need?
I don't understand what is general guideline in such situations,
because it's common case when I need create some mutable copy of
const or immutable struct data to work with.
