Really? You see those as the only two alternatives? Either teachers can say anything about any student on any forum OR they can say nothing about any student ever?

Ah I see what you mean now. Actually I think you've hit upon the key feature of Design by Contract that most people miss. It's not just tossing assertions all over your code. It's a design discipline that shapes the way you write the system, and that's why it's good at finding design problems.

Actually Design by Contract is a design discipline, not a bunch of error checks. It's a bit like programming without gotos: the benefit comes not from avoiding typing "goto" into your source code, but rather from the style of reasoning you use when you learn the proper alternatives.

The "definition of correct" is the system working the way it should. I'm not sure what you're suggesting here: that a system should stick with the original, possibly flawed, contracts rather than fix them to operate properly? That once you make an error in a contract, you should live with it forever? I fail to see how that perspective is helpful or realistic, and, forgive me if I'm wrong, but I suspect you may be lacking in practical experience with Design by Contract.

Contracts can easily have bugs. That shouldn't be too hard to imagine. You could easily have a postcondition "ensure item[index] == 123" when "index" is out of bounds, or when you meant to write "0x123", or when the array is actually called "items".

The fact that contracts can have bugs doesn't negate their value any more than the same fact about software negates software's value.

Uh... unless you care about something other than resolution. Like desk space, or weight, or power consumption.

I know I find it increasingly frustrating to contribute because whatever you add, there's always someone waiting to revert it immediately without any attempt at compromise or discussion.

I also have to say that I think people will find it humourous 50 years from now when they look back at comments from 2009 about how there's not much new stuff to add. That's a bit like the fellow who wanted to close the patent office in 1899 because everything had already been invented.