Examples

Supported types

Scala-yaml has built-in support for:

all primitive types
some types from stdlib like Option
collections from stdlib

Primitives

import org.virtuslab.yaml.*

"1".as[Double]
// Right(1)

"aezakmi".as[Double]
// Cannot parse aezakmi as Double

Option

When deserializing, YAML differentiates between empty string and null value. Hence in the following yaml

key1: ""
key2: !!null
key3:

key1 has empty String as value while both key2 and key3 are considered to have null value.

(there is an issue with deriving YamlEncoder instance for Option datatype hence YamlDecoder instead YamlCodec)

import org.virtuslab.yaml.*

case class Keys(key1: String, key2: Option[String], key3: Option[String]) derives YamlDecoder 
"""|key1: ""
   |key2: !!null
   |key3: 
   |""".stripMargin.as[Keys]

List

import org.virtuslab.yaml.*

"""|- 1
   |- !!null
   |- 3
   |""".stripMargin.as[List[Option[Int]]]
// Right(List(Some(1), None, Some(3)))

"""|- 1
   |- 2
   |- 3
   |""".stripMargin.as[List[Int]]
// Right(List(1, 2, 3))

Map

import org.virtuslab.yaml.*

"""|1: one
   |2: two
   |3: three
   |""".stripMargin.as[Map[Int, String]]
// Right(Map(1 -> one, 2 -> two, 3 -> three))

Decoding from unknown type

It is also possible to decode yaml of unknown type. Since yaml consists of: scalars, mappings and sequences one can use:

as[Any] - it will decode yaml into List or Map depending on its structure
as[List] or other sequence datatypes - it will try to decode yaml sequence
as[Map] - similarly, it will try to decode yaml mapping

import org.virtuslab.yaml.*

"""|- 1
   |- !!null
   |- 3
   |""".stripMargin.as[Any]
// Right(List(1, None, 1))

"""|- 1
   |- 2
   |- 3
   |""".stripMargin.as[Any]
// Right(List(1, 2, 3))

Take a closer look at outcome of first snippet, it List(1, None, 1). Since Any doesn't provide any suggestions, scala-yaml will try to construct as precised typed as it can.

import org.virtuslab.yaml.*

"""|1: one
   |2: two
   |3: three
   |""".stripMargin.as[Any]
// Right(Map(1 -> one, 2 -> two, 3 -> three))

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