#571 – Covariance in Programming Languages

In programming languages, the idea of covariance has to do with whether the ordering of a set of elements is preserved after calling some function that transforms each element.

Consider a set of elements and a function F that accepts as input a member of the set and returns a member of the set.  I.e. X’ = F(X), where both X and X’ are members of the set.

We describe a function as covariant if preserves the ordering of elements of the set passed to it.  If we have two members of our set, X and Y, and X <= Y, then the function F is covariant if F(X) <= F(Y).

For example, the function F(X) = 2X is covariant with respect to the set of integers.  If X <= Y, then 2X <= 2Y, for any X and Y integer values that you pick.

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About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

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