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

[d-bugmail at puremagic.com]

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



--- Comment #33 from Walter Bright <bugzilla at digitalmars.com> 2012-05-04 11:42:40 PDT ---
(In reply to comment #32)
> (In reply to comment #30)
> > fizzbuzz() clearly has a bug. It will fail if given an A which isn't actually a
> > B.
> 
> Exactly.  fizzbuzz is calling a method of A, not a method of B.  As such, as
> I've already said, it must conform to A's API, but it is failing to do so.

First off, if fizzbuzz() is passed an A, then it will (correctly) fail. Where's
the bug in the contract design? Secondly, the -1 may not be a literal, it may
be a value computed from B, as in:


 class A {
     void foo(int x) in { assert(x > 0); } body {}
     int bar() { return 1; }
 }

 class B : A {
     void foo(int x) in { assert(x > -2); } body {}
     int bar() { return -1; }
 }

 void fizzbuzz(A a) {
     a.foo(bar());
 }

So, clearly is NOT required that a.foo(arg) pass A.foo's contract.

The design of OOP and contracts is sound. Correct programs will pass, and
incorrect programs will fail. I don't see any "corner cases" otherwise.

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