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package com.wellfactored.playbindings

/**
 * Defines an interface that can take a value of type V and wrap it in an
 * instance of type W, and take a W and unwrap it to a V.
 *
 * For example, if W is `case class Foo(value:String) extends AnyVal` then
 * we can create an instance of ValueWrapper as:
 *
 * {{{
 * implicit val FooValueWrapper extends ValueWrapper[String, Foo] {
 *   def wrap(v:String) : Either[String, Foo] = Right(Foo(v))
 *   def unwrap(f:Foo) = foo.value
 * }
 * }}}
 *
 * The `wrap` method returns `Either[String, W]` to allow for situations where
 * the V being passed in cannot be converted to a W.
 *
 * By making this a type class we can re-use instances of it in a number of
 * places, for example to remove a great deal of boilerplace when creating
 * instances of Play Framework json formatters and url path binders for
 * case classes that extend AnyVal
 *
 * @tparam V the type of the value that is being wrapped
 * @tparam W the type of the wrapper instance
 */
trait ValueWrapper[V, W] {
  /*
  * @return a Right with the wrapped value, or a Left with an error message if
  * this value cannot be wrapped
   */
  def wrap(v: V): Either[String, W]

  def unwrap(w: W): V
}