• Dan (21/21) Aug 16 2001 Hi,
• Walter (3/24) Aug 16 2001 contracts.

Dan <zakaib mda.ca> writes:

Hi,

I read the section on contracts and I think I noticed a problem with 
regards to inheritance:

"
In, Out and Inheritance
If a function in a derived class overrides a function in its super 
class, then the in contracts must be satisified for each base function. 
Overriding functions then becomes a process of tightening the in contracts.
Conversely, only one of the out contracts needs to be satisified, so 
overriding functions becomes a processes of loosening the out contracts.
"

I believe that is backwards, in contracts should be loosened (or the 
same) and out contracts should be tightened (or the same). Allow me to 
quote from Meyer's "Object-Oriented Software Contruction" Section 16.1:

"
Assertion Redeclaration Rule (1)
  A routine redeclararation may only replace the original precondition 
by one equal or weaker, and the original postcondition by one equal or 
stronger.
"

Dan

"Walter" <walter digitalmars.com> writes:

Good catch. I think I did get that inverted in the doc. Thanks! -Walter

"Dan" <zakaib mda.ca> wrote in message news:3B7C1976.80108 mda.ca...
 Hi,

 I read the section on contracts and I think I noticed a problem with
 regards to inheritance:

 "
 In, Out and Inheritance
 If a function in a derived class overrides a function in its super
 class, then the in contracts must be satisified for each base function.
 Overriding functions then becomes a process of tightening the in

contracts.
 Conversely, only one of the out contracts needs to be satisified, so
 overriding functions becomes a processes of loosening the out contracts.
 "

 I believe that is backwards, in contracts should be loosened (or the
 same) and out contracts should be tightened (or the same). Allow me to
 quote from Meyer's "Object-Oriented Software Contruction" Section 16.1:

 "
 Assertion Redeclaration Rule (1)
   A routine redeclararation may only replace the original precondition
 by one equal or weaker, and the original postcondition by one equal or
 stronger.
 "

 Dan