Struct-typing in Phobos

[Dicebot]

I find structs completely superior to classes as design base and 
only resort to latter if find myself in need of polymorphic 
behavior. There is an issue of bad constraint error messages but 
that is exactly that - implementation flaw that needs to be 
fixed, not a conceptual flaw.

Mostly agree with Jakob have said, few extra tips:

1) you can use `foo(T : Stuff)(T t)` instead of `foo(T)(T t) if 
(isImplicitlyConvertible!(T, Stuff))`

2) You can extend structs no only with UFCS but also via `alias 
this`:

struct One
{
     void foo() {}
}

struct Two
{
     private One one;
     alias one this;

     void bar() {}
}

void main()
{
     Two two;
     two.foo(); two.bar();
}

Aliasing members as this can be considered a form of single 
inheritance in this context.