Conformance

Question 1

What is the meaning of the “Same or better” principle?

Answer 1

An overriding method should have at least the same functionality as the overridden method.
Namely:
Overriding should not pose surprises to client

Question 2

What is the liskov substitution principle?

Answer 2

functions that use pointers or references to base classes
must be able to use objects of derived classes -
without knowing it!

Question 3

What’s the meaning of no-variance?

Answer 3

The argument’s type cannot be changed

Question 4

What’s the meaning of Covariance?

Answer 4

Change argument’s type in the same direction as the inheritance direction

Question 5

What’s the meaning of Contravariance?

Answer 5

Change argument’s type in the opposite direction of the inheritance direction

Question 6

is function arguments covariance safe?

Answer 6

No.

Question 7

is function arguments contravariance safe?

Answer 7

Yes

Question 8

is return type covariance safe?

Answer 8

yes

Question 9

How variance works in c++ and java?

Answer 9

return type - covariance
arguments - no-variance
If a method has a covariant argument, It does not override the “old” method
in java: overloading
in c++: hiding

Question 10

What’s the diffrence between java, smalltalk and c++ regarding access conformance?

Answer 10

smalltalk - all methods are public.
java - can only improve visibility in a subtype
c++ - not enforced.

Question 11

What does design by contract means?

Answer 11

A method can declare pre-conditions
-   Expected arguments values
A method can declare post-conditions
-    Guaranteed return value
A class can declare invariants
-   Object’s state (when stable)
Contract is checked at run time
-   Like an assert – exception thrown upon failure

Question 12

What is the conformance in design by contract?

Answer 12

Pre-condition Conformance-
Overriding method must demand the same or less from its client (preconditions are or’ed).

Post-condition Conformance-
Overriding method must ensure the same or more to its client (post-conditions are and’ed).

Invariants Conformance-
Derived must keep Base invariants; can add invariants guarding any newly introduced fields.