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

[d-bugmail at puremagic.com]

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


Stewart Gordon <smjg at iname.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |


--- Comment #21 from Stewart Gordon <smjg at iname.com> 2012-05-03 17:20:19 PDT ---
Let's look at it another way.  The relevant basic principle of inheritance is
the ability to extend the functionality of a class, i.e. add to what can be
done with its objects.

There are two main ways in which a class B can extend the functionality of a
class A:
(a) adding new methods
(b) widening the range of legal inputs to an existing method

In order for a class user to take advantage of (a), it must have a reference of
type B.  You can't call these new methods through a reference of type A.

To be sound, (b) should be equally subject to this requirement.

It might be Walter's decision that, in D, (b) is going to continue to be exempt
from this requirement.  But then it's a WONTFIX.  But otherwise, it's
reasonable that some people may want (b) to be subject to the requirement,
while others may want it to be exempt from it.  It's an open matter of debate,
therefore whatever this issue is, it certainly isn't INVALID.

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