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.
> ./sbt bijection-core/console scala> import com.twitter.bijection._ 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].
import com.twitter.bijection._ 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) res2: com.twitter.bijection.package.@@[String,com.twitter.bijection.Rep[Int]] = 100
invert to reverse the transformation:
scala> Bijection.invert[Int, String @@ Rep[Int]](res2) res3: Int = 100
import Conversion.asMethod you can use
.as[T] to use an available Bijection/Injection to
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: Try[Long] = Success(123456789)
When you have bijections between a path of items you can
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(res0) res1: Try[Long] = Success(243)
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
- all numeric types <-> String (Injections)
- Bijections for all
asJavapairs provided by scala.collection.JavaConverters
- String <-> utf8 encoded bytes
Class[T]<-> String (Injection)
A => B<->
C => D(function conversion)
- Bijection/Injection builders for all tuples. (
(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:
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.
Community and Documentation
This, and all github.com/twitter projects, are under the Twitter Open Source Code of Conduct. Additionally, see the Typelevel Code of Conduct for specific examples of harassing behavior that are not tolerated.
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.
Bijection modules are available on maven central. The current groupid and version for all modules is, respectively,
Current published artifacts are
Every artifact is published against Scala
"2.11". To pull in the jars, make sure to add your desired scala version as a suffix, ie:
- Oscar Boykin http://twitter.com/posco
- Marius Eriksen http://twitter.com/marius
- Sam Ritchie http://twitter.com/sritchie
Copyright 2012 Twitter, Inc.
Licensed under the Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0