7 Jul 2004 chalst   » (Master)

Liskov Substitution Property
graydon writes on the failure of object oriented programming languages to enforce the Liskov substitution property. I tend to make very limited use of OO in my programming, but I wonder how bad the lack here is. Oleg's example is easy to solve: what one would do is have each class inherit from a common abstract class; my guess is that LSP violations hardly ever occur in code written by experienced OO programmers (an analogous point would be violations of occurs-check in Prolog code: it happens rarely enough that Prolog implementors think it is not worth the overhead of defining unification to detect occurs check violations).

Graydon also says this issue lends further evidence to my belief that language design is actually regressing: even better evidence for this is the corruption of `lexical' scoping in Python, a disease which I note has spread (hint: lexical scope is entirely determined by the syntactic structure of the source code).

Copenhagen Consensus
In a piece of underreported news, Bjorn Lomborg has announced he will step down as chair of the Danish Environmental Assessment Institute. John Quiggin has two pieces assessing his major achievement in this time: part one criticising the composition of the panel, and part two criticising the idea of trade offs implicit in the latter. He's surely right on the first point, but on the second, I'm not sure that coming up with a cost-benefit ranking does presuppose the picture of trade offs Quiggin criticises; instead it can tell you in what direction we should be pressuring for change.

On a general point, I think Quiggin is the best blogger on matters of environmental economics.

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