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author | Loic Descotte <loic.descotte@gmail.com> | 2017-11-11 08:04:42 +0100 |
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committer | Loic Descotte <loic.descotte@gmail.com> | 2017-11-11 08:24:30 +0100 |
commit | 2cd897dd1bb05981fac1fc9d61ee32f26a16c35b (patch) | |
tree | c2fb5fa0a884f501e053eb979e6dd0862f54336e /examples/shared/src/main/scala/default.scala | |
parent | efe98a7d0b134415f3da0e7a7c3cb6ca5f2b44c4 (diff) | |
download | magnolia-2cd897dd1bb05981fac1fc9d61ee32f26a16c35b.tar.gz magnolia-2cd897dd1bb05981fac1fc9d61ee32f26a16c35b.tar.bz2 magnolia-2cd897dd1bb05981fac1fc9d61ee32f26a16c35b.zip |
scalajs cross build
Diffstat (limited to 'examples/shared/src/main/scala/default.scala')
-rw-r--r-- | examples/shared/src/main/scala/default.scala | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/examples/shared/src/main/scala/default.scala b/examples/shared/src/main/scala/default.scala new file mode 100644 index 0000000..4c1b634 --- /dev/null +++ b/examples/shared/src/main/scala/default.scala @@ -0,0 +1,35 @@ +package magnolia.examples + +import magnolia._ +import scala.language.experimental.macros + +/** typeclass for providing a default value for a particular type */ +trait Default[T] { def default: T } + +/** companion object and derivation object for [[Default]] */ +object Default { + + type Typeclass[T] = Default[T] + + /** constructs a default for each parameter, using the constructor default (if provided), + * otherwise using a typeclass-provided default */ + def combine[T](ctx: CaseClass[Default, T]): Default[T] = new Default[T] { + def default = ctx.construct { param => + param.default.getOrElse(param.typeclass.default) + } + } + + /** chooses which subtype to delegate to */ + def dispatch[T](ctx: SealedTrait[Default, T])(): Default[T] = new Default[T] { + def default: T = ctx.subtypes.head.typeclass.default + } + + /** default value for a string; the empty string */ + implicit val string: Default[String] = new Default[String] { def default = "" } + + /** default value for ints; 0 */ + implicit val int: Default[Int] = new Default[Int] { def default = 0 } + + /** generates default instances of [[Default]] for case classes and sealed traits */ + implicit def gen[T]: Default[T] = macro Magnolia.gen[T] +} |