invariant

The two main problems with this approach is it is not rotation-invariant and it does not work well if the image is damaged or added to.

I dont hide it under the getter/setter carpet, unless it actually helps me enforce some specific invariant.

" What I mean by "leveraged" is that some significant guarantee or invariant is achieved through a complicated contract between two different objects.

Safeness of the kind described in the article does not come at the cost of performance -- all type checks, invariant conditions and general formal proofs of correctness are determined at compile time.

And ignore the guy who says he won't pay for it because his unwillingness to pay for your products or services is invariant under any course of action you take and can hence be dropped totally from your Karnaugh map."

I don't know of any programming mode that could be made to meet this invariant easily; consider the case: /* this code is bad: int i = 0; */ If we had two threads fontifying this block, and the bounds were set to thread 1 = line 1, thread 2 = line 2, the results are going to be wrong.

Bird's idea is that we can establish certain mathematical rules which allow us to transform "the simplest thing which could possibly be correct" to an efficient program through a series of steps, each one maintaining correctness as an invariant.