From: http://www.digitalmars.com/d/dbc.html

> In, Out and Inheritance
> If a function in a derived class overrides a function in its  super class,
> then only one of  the in contracts of the base functions must be satisified
> Overriding  functions then becomes a process of loosening the in  contracts.

In OOSC2 (P573) Meyer (who invented Design by Contract) says:

> Assertion Redeclaration rule
> A routine redeclreation may only replace the original precondition
> by one equal or weaker, and the original postcondition by one equal or storgner.

I am intersted to know why in D, "one of the in contracts of the base functions
must
be specified". Why must any of the "contracts of the base functions" be
satisifed at
all if the new precondition is satisfied.
If an overriden function has a new precondition it should be or-ed with
the existing preconditions. Is this the intention in D?

Sam O'Connor

<samoconnor@mac.com> wrote in message news:c600ck$203e$1@digitaldaemon.com...
> From: http://www.digitalmars.com/d/dbc.html
>
> > In, Out and Inheritance
> > If a function in a derived class overrides a function in its  super
class,
> > then only one of  the in contracts of the base functions must be
satisified
> > Overriding  functions then becomes a process of loosening the in
contracts.
>
> In OOSC2 (P573) Meyer (who invented Design by Contract) says:
>
> > Assertion Redeclaration rule
> > A routine redeclreation may only replace the original precondition
> > by one equal or weaker, and the original postcondition by one equal or
storgner.
>
> I am intersted to know why in D, "one of the in contracts of the base
functions
> must
> be specified". Why must any of the "contracts of the base functions" be
> satisifed at
> all if the new precondition is satisfied.
> If an overriden function has a new precondition it should be or-ed with
> the existing preconditions. Is this the intention in D?

Yes, or-ing the preconditions is the same thing as stating that any of the preconditions need to be satisified, which is the same thing as what Meyer writes.