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Postings from March 2005
HaloO Luke, you wrote: > The words 'covariant' and 'contravariant' in this context seem like > voodoo math. Please explain what you mean. 'Co' means together like in coproduction. And 'contra' is the opposite as in counterproductive. With instanciating parametric types the question arises how a subtype relation between instanciating types propagates to the template. E.g with Int <: Num, covariance would result in Array[Int] <: Array[Num]. Referential classes are actually quite difficult because upon write they are contravariant and covariant when read! So a third case of uncomparable types is needed as well, or it is the default if nothing else is specified. > That's not true. I don't believe it would be an error to specify > all nine combinations. Ohh, sorry. Of course implementing all is fine as well. But a bit tedious for larger collections of classes. MfG -- TSa (Thomas Sandlaß)Thread Previous | Thread Next