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Break OO privacy: Difference between revisions
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=={{header|Ada}}==
One of the great criticisms of Pascal was "there is no escape". The reason was that sometimes you have to convert the incompatible.
<lang Ada>package OO_Privacy is
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end OO_Privacy;</lang>
When we later define an object C of type Confidential_Stuff, we can't read read the password stored in C -- except by breaking / bypassing OO privacy rules.
=== Using Unchecked_Conversion ===
One way to read the password is by using the generic function Unchecked_Conversion:
<lang Ada>with OO_Privacy, Ada.Unchecked_Conversion, Ada.Text_IO;
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<pre>The secret password is "default!"</pre>
=== Child Packages ===
Another way to bypass privacy is using a child package. Ada child packages have access to their parents' private data structures (somewhat similar to "friends" in C++"):
<lang Ada>package OO_Privacy.Friend is -- hhild package of OO.Privacy
function Get_Password(Secret: Confidential_Stuff) return String;
end OO_Privacy.Friend;</lang>
<lang Ada>package body OO_Privacy.Friend is -- implementation of the child package
function Get_Password(Secret: Confidential_Stuff) return String is
(Secret.Password);
end OO_Privacy.Friend;</lang>
Now here is the program that uses the child package, to read the secret:
<lang Ada>with OO_Privacy.Friend, Ada.Text_IO;
procedure Bypass_OO_Privacy is
C: OO_Privacy.Confidential_Stuff; -- which password is hidden inside C?
begin
Ada.Text_IO.Put_Line("Password: """ &
OO_Privacy.Friend.Get_Password(C) &
"""");
end Bypass_OO_Privacy;</lang>
Once again, we have been too lazy to overwrite the default password:
<pre>Password: "default!"</pre>
In fact, the password has to be the default one, because we cannot change the password. For that purpose, we would have to write a setter procedure, and either include it in the package OO_Privacy, or in a child package of OO_Privacy. (Or we could use Unchecked_Conversion to overwrite the default password -- but that is bad style.)
=={{header|C sharp}}==
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