Variant

Template for a codec for a sum type A.

Each constructor of A should get assigned a unique index when implementing this class. It is used to tag XML trees, so that the correct decoding function can be chosen.

In addition to the contract of Codec, instances of this class must also preserve the index, that is, any index returned by enc must produce a valid decoding function in dec.

Using this is a two-step process: First, create an object extending from this abstract and implement enc and dec accordingly. Second, call toCodec with an arbitrary tag on that object to obtain the actual codec. This process exists to work around a bug in the Scala compiler.

Example usage

new Variant[Option[A]] {
  def enc(env: Environment, a: Option[A]): (Int, env.XMLTree) = a match {
    case Some(a) => (0, Codec[A].encode(env)(a))
    case None    => (1, Codec[Unit].encode(env)(()))
  }
  def dec(env: Environment, idx: Int): Option[env.XMLTree => XMLResult[Option[A]]] = idx match {
    case 0 => Some(Codec[A].decode(env)(_).right.map(Some.apply))
    case 1 => Some(Codec[Unit].decode(env)(_).right.map(_ => None))
    case _ => None
  }
} toCodec "option"

Note the closing call to toCodec. The return type annotations are required for Scala 2.10.x.

Footnote

The preferred interface would look roughly like this:

def variant[A](env: Environment)(enc: A => (Int, env.XMLTree), dec: Int => Option[env.XMLTree => Result[A]], tag: String): Codec[A]

It can't be realised because some Scala versions have trouble establishing equivalence between path-dependent types.

Linear Supertypes

AnyRef, Any

Instance Constructors

new Variant()

Abstract Value Members

abstract def dec(env: Environment, idx: Int): Option[(XMLTree) ⇒ XMLResult[A]]

Given an index, produce the corresponding decoding function or nothing if the index is out of bounds.
abstract def enc(env: Environment, a: A): (Int, XMLTree)

Encode a value of the sum type into a tree and the index.

Concrete Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def ##(): Int

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
def hashCode(): Int

Definition Classes
AnyRef → Any
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def toCodec(tag: String): Codec[A]

Turn an instance of this object into an actual Codec.
def toString(): String

Definition Classes
AnyRef → Any
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )

Related Doc: package Codec

abstract class Variant[A] extends AnyRef

Instance Constructors

new Variant()

Abstract Value Members

abstract def dec(env: Environment, idx: Int): Option[(XMLTree) ⇒ XMLResult[A]]

abstract def enc(env: Environment, a: A): (Int, XMLTree)

Concrete Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

final def asInstanceOf[T0]: T0

def clone(): AnyRef

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

def finalize(): Unit

final def getClass(): Class[_]

def hashCode(): Int

final def isInstanceOf[T0]: Boolean

final def ne(arg0: AnyRef): Boolean

final def notify(): Unit

final def notifyAll(): Unit

final def synchronized[T0](arg0: ⇒ T0): T0

def toCodec(tag: String): Codec[A]

def toString(): String

final def wait(): Unit

final def wait(arg0: Long, arg1: Int): Unit

final def wait(arg0: Long): Unit

Inherited from AnyRef

Inherited from Any

Ungrouped