Reversible conversions between types

## 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.

## Examples:

> ./sbt bijection-core/console
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 => Try[A].

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

scala> Injection.invert[Int, String](res0)
res1: Try[Int] = Success(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)

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> 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

scala> injection(123456789L)

scala> injection.invert(res1)
res2: Try[Long] = Success(123456789)

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

scala> import Conversion.asMethod
import Conversion.asMethod

scala> implicit val long2String2Bytes2B64 = connect[Long,String,Array[Byte],Base64String]

scala> 243L.as[Base64String]

scala> long2String2Bytes2B64.invert(res0)
res1: Try[Long] = Success(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/avro <-> Array[Byte] (Injections via bijection-protobuf/bijection-thrift/bijection-avro)
• 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.

## Documentation

To learn more and find links to tutorials and information around the web, check out the Bijection Wiki.

The latest ScalaDocs are hosted on Bijection's Github Project Page.

## Get Involved + Code of Conduct

Pull requests and bug reports are always welcome!

Discussion occurs primarily on the Bijection mailing list. Issues should be reported on the GitHub issue tracker.

We use a lightweight form of project governence inspired by the one used by Apache projects. Please see Contributing and Committership for our code of conduct and our pull request review process. The TL;DR is send us a pull request, iterate on the feedback + discussion, and get a +1 from a Committer in order to get your PR accepted.

The current list of active committers (who can +1 a pull request) can be found here: Committers

A list of contributors to the project can be found here: Contributors

## Maven

Bijection modules are available on maven central. The current groupid and version for all modules is, respectively, "com.twitter" and 0.9.5.

Current published artifacts are

• bijection-core
• bijection-protobuf
• bijection-thrift
• bijection-guava
• bijection-scrooge
• bijection-json
• bijection-util
• bijection-clojure
• bijection-netty
• bijection-avro
• bijection-hbase

Every artifact is published against Scala "2.10", "2.11" and "2.12". To pull in the jars, make sure to add your desired scala version as a suffix, ie:

bijection-core_2.10 or bijection-core_2.11 or bijection-core_2.12.