What is Invariant Good For?

[Peter C. Chapin]

Walter Bright wrote:

> http://www.reddit.com/r/programming/comments/6ui1q/d_what_is_invariant_good_for/

For what it's worth, I agree with some of the posts on the article 
itself that "immutable" would be a better word to describe this concept 
than "invariant." I've done some functional programming and I 
immediately understand what immutable means (and why it is good). With 
invariant I had to read about it first. The word invariant makes me 
think of class invariants and loop invariants... a somewhat different 
concept.

Peter