C# Language Specification

Members

With the exception of partial methods (§10.2.7), the set of members of a type declared in multiple parts is simply the union of the set of members declared in each part. The bodies of all parts of the type declaration share the same declaration space (§3.3), and the scope of each member (§3.7) extends to the bodies of all the parts. The accessibility domain of any member always includes all the parts of the enclosing type; a private member declared in one part is freely accessible from another part. It is a compile-time error to declare the same member in more than one part of the type, unless that member is a type with the partial modifier.

partial class A

{
int x; // Error, cannot declare x more than once

partial class Inner // Ok, Inner is a partial type

{
int y;
}
}

partial class A

{
int x; // Error, cannot declare x more than once

partial class Inner // Ok, Inner is a partial type

{
int z;
}
}

The ordering of members within a type is rarely significant to C# code, but may be significant when interfacing with other languages and environments. In these cases, the ordering of members within a type declared in multiple parts is undefined.

7.