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Reversible conversions between types
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Bijection Build Status

A Bijection is an invertible function that converts back and forth between two different types, with the contract that a round-trip through the Bijection will bring back the original object.

Many Bijections are supplied by default. Use the Bijection object to apply Bijections that are present implicitly:

import com.twitter.bijection._

scala> Bijection[Int, Array[Byte]](100)
res1: Array[Byte] = Array(0, 0, 0, 100)

scala> Bijection[Int, String](100)
res2: String = 100

scala> Bijection[Int, java.lang.Integer](100)
res3: java.lang.Integer = 100

Use invert to reverse the transformation:

scala> Bijection.invert[Int, String](res2)
res4: Int = 100

If you import Bijection.asMethod you can use .as[T] to do the default bijection to T:

scala> import com.twitter.bijection.Bijection.asMethod
import com.twitter.bijection.Bijection.asMethod

res0: String = 1

Bijections can also be composed. As with functions, andThen composes forward, compose composes backward.

This example round-trips a long into a GZipped base64-encoded string:

scala> val bijection = Bijection.long2BigEndian andThen Bijection.bytes2GZippedBase64
bijection: com.twitter.bijection.Bijection[Long,com.twitter.bijection.GZippedBase64String] = <function1>

scala> bijection(123456789L)
res8: com.twitter.bijection.GZippedBase64String = GZippedBase64String(H4sIAAAAAAAAAGNgYGBgjz4rCgBpa5WLCAAAAA==)

scala> bijection.invert(res8)
res9: Long = 123456789

When you have bijections between a path of items you can Bijection.connect them:

scala> import com.twitter.bijection.Bijection.{asMethod, connect}
import com.twitter.bijection.Bijection.{asMethod, connect}

scala> import com.twitter.bijection.Base64String
import com.twitter.bijection.Base64String

scala> implicit val string2Long2Bytes2B64 = connect[String,Long,Array[Byte],Base64String]
string2Long2Bytes2B64: com.twitter.bijection.Bijection[String,com.twitter.bijection.Base64String] = <function1>

scala> "243".as[Base64String]
res0: com.twitter.bijection.Base64String = Base64String(AAAAAAAAAPM=)

res1: String = 243

Supported Bijections

Bijection implicitly supplies Bijections between:

  • all numeric types <-> their boxed java counterparts
  • all numeric types <-> big-endian Array[Byte] encodings
  • all numeric types <-> String
  • Bijections for all asScala, asJava pairs provided by scala.collection.JavaConverters
  • String <-> utf8 encoded bytes
  • Array[Byte] <-> GZippedBytes
  • Array[Byte] <-> Base64String
  • Array[Byte] <-> GZippedBase64String
  • Array[Byte] <-> java.nio.ByteBuffer
  • Class[T] <-> String
  • A => B <-> C => D (function conversion)
  • Bijection builders for all tuples. ((String,Int) <-> (Array[Byte], java.lang.Integer) is built automatically, for example.)

Additionally there is a method to generate Bijections between most of Scala's built in types: Bijection.toContainer[Int,String,List[Int],Vector[String] returns Bijection[List[Int], Vector[String]

If you see a reversible conversion that is not here and related to types in the standard library of Java or Scala, please contribute!


Current version is 0.1.3. groupid="com.twitter" artifact="bijection-core_2.9.2".



Copyright 2012 Twitter, Inc.

Licensed under the Apache License, Version 2.0:

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