why do an assembly with no direct dependency to another assembly have to reference it?

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.

possible duplicate of [Why do I (sometimes) have to reference assemblies referenced by the assembly I reference?](http://stackoverflow.com/questions/10210729/why-do-i-sometimes-have-to-reference-assemblies-referenced-by-the-assembly-i-r) — ChrisF, Feb 12 '13 at 20:41

score 2 · Accepted Answer · answered Feb 12 '13 at 22:38

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.

Dan Hunex · Answer 2 · 2013-02-12T22:38:38.370

0

Well if you did a project reference from Asm3 to Asm1, there is no need to reference the Asm2 to your project. During compilation, it will grab asm2 and put it in the bin folder. However, if you do direct binary reference of Asm1 in Asm3, it needs that asm2 either in bin( because asm1 needs it). This doesn't necessarily require to make a reference to asm2 but but it must be in bin of asm3. Thus, you don't need to do manual copy of Asm2 to bin, therefore you may reference it, it will copy it for you. However, I would do the following,

I will put Asm1, and Asm2 in a folder say dependencies ( for asm3), then I will reference only Asm1 in asm3, during build, asm2 will be copied to the bin directory and you will be good

So In short, your asm1 needs asm2 whereever it goes. That is why you needed it

edited Feb 12 '13 at 22:38

answered Feb 12 '13 at 20:49

Dan Hunex

5,172
2
27
38

thanks for your rep Dan, but I was talking about Asm3 and Asm2 relationship. as you can see in code above when class A isn't a subclass B there's no need to have it as a reference in asm3 and it goes well without it. why is it then? – Jami Feb 12 '13 at 21:30
Yes when you do have the inheritance though Asm1 needs asm2, so if asm3 is to use asm1, for proper function of asm1 , it needs asm2. I also edited the answer a bit to clarify – Dan Hunex Feb 12 '13 at 21:44
I looked at asm3 manifest, there's no asm2 reference in it as I expected. But you're right mate. I got the point. My asm1 needs asm2 whereever it goes – Jami Feb 12 '13 at 22:18

why do an assembly with no direct dependency to another assembly have to reference it?

2 Answers2