Bijection

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

See the current API documentation for more information.

Maven

Current version is 0.3.0. groupid="com.twitter" artifact="bijection-core_2.9.2".

Examples:

scala> Bijection[Int, java.lang.Integer](42)
res0: java.lang.Integer = 42

In addition to Bijection, we have Injection. An Injection embeds a type A in a larger space of type B. Every item from A can be round-tripped through B, but not every B can be mapped to A. So Injection is like a pair of function: A => B, B => Option[A].

import com.twitter.bijection._

scala> Injection[Int, String](100)
res0: String = 100

scala> Injection.invert[Int, String](res0)
res1: Option[Int] = Some(100)

If we want to treat an Injection like a Bijection (over a restricted subspace of the larger set), we use the B @@ Rep[A] syntax, for instance: String @@ Rep[Int]

Bijection[Int, String @@ Rep[Int]](100)
res2: com.twitter.bijection.package.@@[String,com.twitter.bijection.Rep[Int]] = 100

Use invert to reverse the transformation:

scala> Bijection.invert[Int, String @@ Rep[Int]](res2)
res3: Int = 100

If you import Conversion.asMethod you can use .as[T] to use an available Bijection/Injection to T:

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

scala> 1.as[java.lang.Integer]
res6: java.lang.Integer = 1

Bijections and Injections 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 injection = Injection.long2BigEndian andThen Bijection.bytes2GZippedBase64
injection: com.twitter.bijection.Injection[Long,Array[Byte]] = <function1>

scala> injection(123456789L)
res1: com.twitter.bijection.GZippedBase64String = GZippedBase64String(H4sIAAAAAAAAAGNgYGBgjz4rCgBpa5WLCAAAAA==)

scala> injection.invert(res1)
res2: Option[Long] = Some(123456789)

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

scala> import com.twitter.bijection.Injection.connect
import com.twitter.bijection.Injection.connect

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

scala> import Conversion.asMethod
import Conversion.asMethod

scala> implicit val long2String2Bytes2B64 = connect[Long,String,Array[Byte],Base64String]
string2Long2Bytes2B64: com.twitter.bijection.Bijection[String,com.twitter.bijection.Base64String] = <function1>

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

scala> long2String2Bytes2B64.invert(res5)
res1: Option[Long] = Some(243)

Supported Bijections/Injections

Bijection implicitly supplies Bijections between:

• all numeric types <-> their boxed java counterparts
• containers/primitives <-> Json (Injections via bijection-json)
• thrift/protobuf <-> Array[Byte] (Injections via bijection-protobuf/bijection-thrift)
• all numeric types <-> big-endian Array[Byte] encodings (Injections)
• all numeric types <-> String (Injections)
• 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 (Injection)
• A => B <-> C => D (function conversion)
• Bijection/Injection 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!

Serialization via Bufferable

Bufferable[T] handles putting and getting a type T into a ByteBuffer in a composable way. Bufferable[T] instances for all primitives/tuples/containers are provided. Bijections and Injections to any of these types give you binary serialization via Bufferable.

Authors

• Oscar Boykin http://twitter.com/posco
• Marius Eriksen http://twitter.com/marius
• Sam Ritchie http://twitter.com/sritchie

License

Copyright 2012 Twitter, Inc.

Licensed under the Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0