Problematic combination of variance in Scala -

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here example scala course on coursera:, lecture 4.4

class array[+t] {   def update(x: t) = ??? }

this causes error in repl:

error: covariant type t occurs in contravariant position in type t of value x

and on slides, martin says "problematic combination". why so?

this explained in "variance , arrays" section of http://www.artima.com/pins1ed/type-parameterization.html (from programming in scala odersky, venners, , spoon).


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