com.avsystem.commons.meta.MetadataCompanion.scala Maven / Gradle / Ivy

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package com.avsystem.commons
package meta

import com.avsystem.commons.macros.misc.MiscMacros
import com.avsystem.commons.misc.ImplicitNotFound

import scala.annotation.implicitNotFound

/**
  * Base trait for companion objects of _metadata classes_. A metadata class is a generic class that captures
  * metadata for some Scala type, typically an RPC interface ([[com.avsystem.commons.rpc.RpcMetadataCompanion RpcMetadataCompanion]])
  * or a data type ([[AdtMetadataCompanion]]).
  *
  * @tparam M metadata class constructor
  */
trait MetadataCompanion[M[_]] {
  final def apply[Real](implicit metadata: M[Real]): M[Real] = metadata

  implicit final def fromFallback[Real](implicit fallback: Fallback[M[Real]]): M[Real] = fallback.value

  final class Lazy[Real](metadata: => M[Real]) {
    lazy val value: M[Real] = metadata
  }
  object Lazy {
    def apply[Real](metadata: => M[Real]): Lazy[Real] = new Lazy(metadata)

    // macro effectively turns `metadata` param into by-name param (implicit params by themselves cannot be by-name)
    implicit def lazyMetadata[Real](implicit metadata: M[Real]): Lazy[Real] = macro MiscMacros.lazyMetadata

    @implicitNotFound("#{forNotLazy}")
    implicit def notFound[T](implicit forNotLazy: ImplicitNotFound[M[T]]): ImplicitNotFound[Lazy[T]] =
      ImplicitNotFound()
  }
}

/**
  * Like [[MetadataCompanion]] but allows the metadata class' type parameter to be bounded
  *
  * @tparam Hi higher bound of metadata class' type param
  * @tparam Lo lower bound of metadata class' type param
  * @tparam M  metadata class type constructor
  */
// cannot share code with MetadataCompanion because of binary compatibility problems, must copy
trait BoundedMetadataCompanion[Hi, Lo <: Hi, M[_ >: Lo <: Hi]] {
  final def apply[Real >: Lo <: Hi](implicit metadata: M[Real]): M[Real] = metadata

  implicit final def fromFallback[Real >: Lo <: Hi](implicit fallback: Fallback[M[Real]]): M[Real] = fallback.value

  final class Lazy[Real >: Lo <: Hi](metadata: => M[Real]) {
    lazy val value: M[Real] = metadata
  }
  object Lazy {
    def apply[Real >: Lo <: Hi](metadata: => M[Real]): Lazy[Real] = new Lazy(metadata)

    // macro effectively turns `metadata` param into by-name param (implicit params by themselves cannot be by-name)
    implicit def lazyMetadata[Real >: Lo <: Hi](implicit metadata: M[Real]): Lazy[Real] = macro MiscMacros.lazyMetadata

    @implicitNotFound("#{forNotLazy}")
    implicit def notFound[T >: Lo <: Hi](implicit forNotLazy: ImplicitNotFound[M[T]]): ImplicitNotFound[Lazy[T]] =
      ImplicitNotFound()
  }
}