invariance Questions

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Could you please explain using small and simple TypeScript examples what is Variance, Covariance, Contravariance, Bivariance and Invariance?

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I've read some articles about Covariance, Contravariance, and Invariance in Java, but I'm confused about them. I'm using Java 11, and I have a class hierarchy A => B => C (means that C is a s...

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After writing this piece of code module type TS = sig type +'a t end module T : TS = struct type 'a t = {info : 'a list} end I realised I needed info to be mutable. I wrote, then : module type...
Reno asked 9/11, 2016 at 15:10

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References to wrapper types like &Rc<T> and &Box<T> are invariant in T (&Rc<T> is not a &Rc<U> even if T is a U). A concrete example of the issue (Rust Playg...
Brainwashing asked 1/6, 2016 at 23:50

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Reviewing Java 8 Stream API design, I was surprised by the generic invariance on the Stream.reduce() arguments: <U> U reduce(U identity, BiFunction<U,? super T,U> accumulator, Binary...
Pamper asked 28/2, 2016 at 9:18

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The following code in Julia: function foo(a::Vector{AbstractString}) end foo(["a"]) gives the following error: ERROR: MethodError: no method matching foo(::Array{String,1}) Closest candidates...
Scrubland asked 30/1, 2014 at 19:32
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