Parametric Polymorphism
type variables


Task

Write a small example for a type declaration that is parametric over another type, together with a short bit of code (and its type signature) that uses it.



A good example is a container type, let's say a binary tree, together with some function that traverses the tree, say, a map-function that operates on every element of the tree.

This language feature only applies to statically-typed languages.




class Tree<T> {
  var value: T?
  var left: Tree<T>?
  var right: Tree<T>?
 
  func replaceAll(value: T?) {
    self.value = value
    left?.replaceAll(value)
    right?.replaceAll(value)
  }
}