Best of 2015

The blog posts Hacker News loved most in 2015. 3,426 posts.

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1914

Covariance and Contravariance

Subtypes and supertypes are a common part of modern programming. Covariance and contravariance tell us where subtypes are accepted and where supertypes are accepted in place of the original type. This shows up frequently in most of the programming most of us do, but many developers are unaware of the concepts beyond a…