#generic-classes #scala
subtyping of generic types is *invariant*. This means that if we have a stack of characters of type Stack[Char] then it cannot be used as an integer stack of type Stack[Int]. This would be unsound because it would enable us to enter true integers into the character stack.
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Generic Classes - Scala Documentationpe.
Here are some usage examples:
object GenericsTest extends App {
val stack = new Stack[Int]
stack.push(1)
stack.push('a')
println(stack.top)
stack.pop()
println(stack.top)
}
The output of this program will be:
97
1
Note: <span>subtyping of generic types is *invariant*. This means that if we have a stack of characters of type Stack[Char] then it cannot be used as an integer stack of type Stack[Int]. This would be unsound because it would enable us to enter true integers into the character stack. To conclude, Stack[T] is only a subtype of Stack[S] if and only if S = T. Since this can be quite restrictive, Scala offers a type parameter annotation mechanism to control the subtyping Summary
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