} } } So far, so good...

Odnośniki

Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.
out there, for, as far as I could see, the sole purpose of landing soldiers and custom-house officers...
To change the font style, click Bold or Italic in the Property inspector, or choose a font style (Bold, Italic, Underline, and so on) from the Text > Style submenu...
Na su wa siê py ta nie: dla cze go masz p³aciæ za coœ, co mo¿esz mieæ za dar mo? Czy Tim O'Reilly po stra da³ zmys³y i wy da je coœ, co ka ¿dy mo¿e so bie sam wy dru ko...
that came from his lips, and they kept saying, "Isn't this Joseph's son?"4:23-27 - So he said to them, "I expect you will quote this proverb to me,'Cure yourself,...
So we went outside, and I asked if Tyler wanted it in the face or in the stomach...
and be so angry that they’d take it out on anyone who happened to have been around at the time...
Say goodbye, goodbye to whisky,Lordy, so long to gin,Say goodbye, goodbye to whiskyLordy, so long to gin,I just want me reefers,I just...
- Z przyjemnością, pani O'Neill - zgodził się uprzejmie...
60 8
Ziemniaki napeBnione farszem uBo|y w gBbokiej brytfannie z niewid k ilo[ci oleju i wody

Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.

But now the versioning trouble begins. The author of Base produces a new version, and adds its own F method.
22
Copyright  Microsoft Corporation 1999-2000. All Rights Reserved.
Chapter 1 Introduction
// Author A
namespace A
{
class Base
// version 2
{
public virtual void F() {
// added in version 2
System.Console.WriteLine("Base.F");
}
}
}
This new version of Base should be both source and binary compatible with the initial version. (If it weren’t possible to simply add a method then a base class could never evolve.) Unfortunately, the new F in Base makes the meaning of Derived’s F is unclear. Did Derived mean to override Base’s F? This seems unlikely, since when Derived was compiled, Base did not even have an F! Further, if Derived’s F does override Base’s F, then does Derived’s F adhere to the contract specified by Base? This seems even more unlikely, since it is pretty darn difficult for Derived’s F to adhere to a contract that didn’t exist when it was written. For example, the contract of Base’s F might require that overrides of it always call the base. Derived’s F could not possibly adhere to such a contract since it cannot call a method that does not yet exist.
In practice, will name collisions of this kind actually occur? Let’s consider the factors involved. First, it is important to note that the authors are working completely independently – possibly in separate corporations – so no collaboration is possible. Second, there may be many derived classes. If there are more derived classes, then name collisions are more likely to occur. Imagine that the base class is Form, and that all VB, VC++ and C#
developers are creating derived classes – that’s a lot of derived classes. Finally, name collisions are more likely if the base class is in a specific domain, as authors of both a base class and its derived classes are likely to choose names from this domain.
C# addresses this versioning problem by requiring developers to clearly state their intent. In the original code example, the code was clear, since Base did not even have an F. Clearly, Derived’s F is intended as a new method rather than an override of a base method, since no base method named F exists.
// Author A
namespace A
{
class Base
{
}
}
// Author B
namespace B
{
class Derived: A.Base
{
public virtual void F() {
System.Console.WriteLine("Derived.F");
}
}
}
If Base adds an F and ships a new version, then the intent of a binary version of Derived is still clear –
Derived’s F is semantically unrelated, and should not be treated as an override.
However, when Derived is recompiled, the meaning is unclear – the author of Derived may intend its F to override Base’s F, or to hide it. Since the intent is unclear, the C# compiler produces a warning, and by default makes Derived’s F hide Base’s F – duplicating the semantics for the case in which Derived is not recompiled. This warning alerts Derived’s author to the presence of the F method in Base. If Derived’s F is semantically unrelated to Base’s F, then Derived’s author can express this intent – and, in effect, turn off the warning – by using the new keyword in the declaration of F.
Copyright  Microsoft Corporation 1999-2000. All Rights Reserved.
23
C# LANGUAGE REFERENCE
// Author A
namespace A
{
class Base
// version 2
{
public virtual void F() { // added in version 2
System.Console.WriteLine("Base.F");
}
}
}
// Author B
namespace B
{
class Derived: A.Base
// version 2a: new
{
new public virtual void F() {
System.Console.WriteLine("Derived.F");
}
}
}
On the other hand, Derived’s author might investigate further, and decide that Derived’s F should override Base’s F, and clearly specify this intent through specification of the override keyword, as shown below.
// Author A
namespace A
{
class Base
// version 2
{
public virtual void F() { // added in version 2
System.Console.WriteLine("Base.F");
}
}
}
// Author B
namespace B
{
class Derived: A.Base
// version 2b: override
{
public override void F() {
base.F();
System.Console.WriteLine("Derived.F");
}
}
}
The author of Derived has one other option, and that is to change the name of F, thus completely avoiding the name collision. Though this change would break source and binary compatibility for Derived, the importance of this compatibility varies depending on the scenario. If Derived is not exposed to other programs, then changing the name of F is likely a good idea, as it would improve the readability of the program – there would no longer be any confusion about the meaning of F.
1.18 Attributes C# is a procedural language, but like all procedural languages it does have some declarative elements. For example, the accessibility of a method in a class is specified by decorating it public, protected, internal, protected internal, or private. Through its support for attributes, C# generalizes this capability, so that programmers can invent new kinds of declarative information, specify this declarative information for various program entities, and retrieve this declarative information at run-time. Programs specify this additional declarative information by defining and using attributes.
24
Copyright  Microsoft Corporation 1999-2000. All Rights Reserved.