Question

I’m quite new to c# programming.
So lets assume we have two assemblies Asm1, Asm2 in which two classes are defined as Follows:

//Asm1
namespace ClassLibrary1
{
public class A//: B
  {
    B b = new B { i = 2};
    public int MyProperty { get { return b.i; } }
  }
}

//Asm2
namespace ClassLibrary2
{
  public class B
  {
    public int i;
  } 
}

Asm1 references Asm2
Now we have a runnable assembly say,asm3, that uses Asm1 with following piece of code:

//Asm3
A a = new A();
System.Console.Write(a.MyProperty.ToString());

the above codes compiles right with no error.

But things go wrong when we make little change in class A and have it inherited from class B.
In this case line: A a = new A(); doesn’t compile and produces error.
But when we add asm2 as a reference to asm3 it works. please tell me why is that.
why do an assembly ,with no direct dependency to another assembly, have to reference it?
thanks in advance.

Answer 1

In this case the compiler requires access to the assembly where the base class of a type that you use (namely A), is declared. The exact rules are somewhat complex.

It is reported that with .NET 4.0 and Visual Studio 2010, if you in one assembly inherited a class from a second assembly which exposed types from an unreferenced third assembly (and your own project did not expose any of these types), it would work fine. But when upgrading to .NET 4.5 and Visual Studio 2012, the same code and reference combination fails, and you must refer the third assembly.