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Type safety all the way from configuration spec to configuration access in Scala
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Cfg

Implemented using Scalameta, Cfg is an annotation that allows to specify the schema of your application or library configuration using case classes and inner vals and objects. As a Typesafe Config wrapper, the Cfg annotation generates an apply(c: com.typesafe.config.Config) method in the companion object to instantiate your case class from a given Typesafe Config object. With Cfg you enjoy type safety all the way from configuration spec to configuration access along with all the typical associated features of your IDE related with code completion, navigation, and refactoring.

Cfg supports all types handled by Typesafe Config, which, in Scala, are represented with the standard types
String, Int, Long, Double, Boolean, scala.concurrent.duration.Duration, SizeInBytes (alias for Long), along with List[T] and Option[T] (where T is, recursively, any supported type).

Usage

In your build.sbt:

libraryDependencies += "com.github.carueda" %% "cfg" % "0.3.0" % "provided"

addCompilerPlugin(
  ("org.scalameta" % "paradise" % "3.0.0-M8").cross(CrossVersion.full)
)

Use the Cfg annotation to specify the schema of your configuration:

import carueda.cfg._

@Cfg
case class SimpleCfg(int: Int, str: String)

Use any usual Typesafe Config mechanism to load a concrete configuration, for example:

val conf = com.typesafe.config.ConfigFactory.parseString(
  """
  int = 1
  str = "Hobbes"
  """)

Then, just create the wrapper and enjoy the benefits:

val cfg = SimpleCfg(conf)

cfg.int  ==> 1
cfg.str  ==> "Hobbes"

Default values

Just initialize the entries in your class as you would normally do:

@Cfg
case class WithDefaultCfg(
                      int    : Int       = 21,
                      str    : String    = "someStr",
                      simple : SimpleCfg = SimpleCfg(1, "A")
                    )

val conf = ConfigFactory.parseString("")
val cfg = WithDefaultCfg(conf)
cfg.int  ==> 21
cfg.str  ==> "someStr"
cfg.simple.int  ==> 1
cfg.simple.str  ==> "A"

Optional entries

For completely optional entries (i.e., without any default value), use Option[T]:

@Cfg
case class WithOptCfg(
                      int    : Option[Int],
                      str    : Option[String],
                      simple : Option[SimpleCfg]
                    )

val conf = ConfigFactory.parseString(
  """
  int =  8
  simple {
    int = 1
    str = str
  }
  """)
  
val cfg = WithOptCfg(conf)
cfg.int     ==> Some(8)
cfg.str     ==> None
cfg.simple  ==> Some(SimpleCfg(1, "str"))

Class members

You can also include a body with members in the case class:

@Cfg
case class BarCfg(
                   reqInt : Int,
                   reqStr : String
                 ) {

  object foo {
    val bool : Boolean = $

    object baz {
      val who   : String = "Calvin"
      val other : Int    = $
    }
  }
  val long : Long = $
}

This, in particular, allows to directly embed the specification of inner objects without necessarily having to introduce a class for them. The $ is a placeholder that gets replaced with appropriate extraction logic by the Cfg annotation.

Using BarCfg:

val bar = BarCfg(ConfigFactory.parseString(
  """
  reqInt = 9393
  reqStr = "reqStr"
  long = 1212100
  foo {
    bool = false
    baz {
      long = 1212100
    }
  }
  """))

bar.reqInt        ==> 9393
bar.reqStr        ==> "reqStr"
bar.foo.bool      ==> false
bar.foo.baz.long  ==> 1212100
bar.foo.baz.who   ==> "Calvin"
bar.long          ==> 1212100

Lists

As you would expect, just use List[T]:

@Cfg
case class WithListCfg(
                      ints     : List[Int],
                      strs     : List[String],
                      simples1 : List[SimpleCfg],
                      simpless : List[List[SimpleCfg]]
                    ) {

  val strss   : List[List[String]] = $
  val strsss  : List[List[List[String]]] = $
  val simples2: List[SimpleCfg] = $
}

val conf = ConfigFactory.parseString(
  """
  ints  = [1,2,3]
  strs  = [ hello, world ]
  strss = [
    [ abc, de ]
    [ fgh ]
  ]
  strsss = [
    [
      [ a, b ]
      [ c, d, e ]
    ],
    [
      [ x, y ]
      [ j, k ]
    ]
  ]
  simples1 = [
    { int = 1, str = "1" }
  ]
  simpless = [[
    { int = 9, str = "9" }
  ]]
  simples2 = [
    { int = 2, str = "2" },
    { int = 3, str = "3" },
  ]
  """)

val cfg = WithListCfg(conf)
cfg.ints   ==> List(1, 2, 3)
cfg.strs   ==> List("hello", "world")
cfg.strss  ==> List(
  List("abc", "de"),
  List("fgh")
)
cfg.strsss ==> List(
  List(
    List("a", "b"), List("c", "d", "e")
  ),
  List(
    List("x", "y"), List("j", "k")
  )
)
cfg.simples1 ==> List(
  SimpleCfg(1, "1")
)
cfg.simpless ==> List(
  List(SimpleCfg(9, "9"))
)
cfg.simples2 ==> List(
  SimpleCfg(2, "2"),
  SimpleCfg(3, "3")
)

Duration

import scala.concurrent.duration._

@Cfg
case class WithDurationCfg(
                      dur    : Duration,
                      durOpt : Option[Duration],
                      durs   : List[Duration]
                    )

val conf = ConfigFactory.parseString(
  """
  dur = 6h
  durs = [ 3600s, 1d ]
  """)
val cfg = WithDurationCfg(conf)
cfg.dur.toHours  ==> 6
cfg.durOpt  ==> None
cfg.durs.map(_.toHours)  ==> List(1, 24)

Size-in-bytes

This is represented with a long type in the Typesafe Config library. In Cfg, to tell this type apart from a regular Long, use the alias SizeInBytes:

@Cfg
case class WithBytesCfg(
                      size    : SizeInBytes,
                      sizeOpt : Option[SizeInBytes],
                      sizes   : List[SizeInBytes]
                    )

val conf = ConfigFactory.parseString(
  """
  size = 2048K
  sizes = [ 1000, "64G", "16kB" ]
  """)
val cfg = WithBytesCfg(conf)
cfg.size     ==> 2048*1024
cfg.sizeOpt  ==> None
cfg.sizes    ==> List(1000, 64*1024*1024*1024L, 16*1000)

tests

https://github.com/carueda/cfg/tree/master/src/test/scala

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