com.avsystem.commons.serialization.whenAbsent.scala Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of commons-core_2.12 Show documentation

AVSystem commons library for Scala

The newest version!

package com.avsystem.commons
package serialization

/**
  * An alternative way to provide default value for case class parameter used during deserialization with `GenCodec`
  * when its field is missing in data being deserialized. Normally, Scala-level default parameter values are picked
  * up, but you may want to use this annotation instead if you don't want to pollute your Scala classes with
  * unintended default parameter values (i.e. you want a default value *only* for deserialization).
  *
  * {{{
  *   case class HasDefault(@whenAbsent("default") str: String)
  *   object HasDefault extends HasGenCodec[HasDefault]
  * }}}
  *
  * If a parameter has both Scala-level default value and is annotated with `@whenAbsent` then value from annotation
  * takes priority. You can use this to have different source-level default value and different
  * default value for deserialization. You can also leverage this to "remove" default value for deserialization:
  *
  * {{{
  *   case class HasNoDefault(@whenAbsent(throw new Exception) str: String = "default")
  *   object HasDefault extends HasGenCodec[HasDefault]
  * }}}
  *
  * NOTE: [[whenAbsent]] also works for method parameters in RPC framework.
  */
class whenAbsent[+T](v: => T) extends StaticAnnotation {
  def value: T = v
}
object whenAbsent {
  /**
    * If you want your parameter to have _both_ a `@whenAbsent` annotation and a Scala-level default value, you can
    * use this macro to avoid writing the default value twice:
    *
    * {{{
    *   case class Record(@whenAbsent(0) i: Int = whenAbsent.value)
    * }}}
    *
    * This is useful when you want the default value to be collectible by macros (e.g. `OpenApiMetadata` for REST).
    * which is possible only with default value in annotation.
    */
  def value[T]: T = macro macros.misc.WhiteMiscMacros.whenAbsentValue
}