[Issue 6857] Precondition contract checks should be statically bound.

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6857


Walter Bright <bugzilla at digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |
           Severity|enhancement                 |normal


--- Comment #55 from Walter Bright <bugzilla at digitalmars.com> 2012-05-05 17:27:24 PDT ---
Mea culpa.

I read Meyer's book again. Chapter 16.1 "Cutting out the middleman" pg. 575
says:

"A client of MATRIX must satisfy the original (stronger) precondition, and may
only expect the original (weaker) postcondition; even if its request gets
served dynamically by NEW_MATRIX it has no way of benefiting from the broader
tolerance of inputs and tighter precision of results. To get this improved
specification it must declare the matric to be of type NEW_MATRIX, thereby
losing access to other implementations represented by descendants of MATRIX
that are not also descendants of NEW_MATRIX."

(MATRIX is the base class, NEW_MATRIX is the derived class.)

So I'm reopening it as a normal bug.

Unfortunately, I do not currently see a reasonable way of implementing this.
Fortunately, as is it does not inhibit correct programs, it only accepts some
invalid ones.

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