如何使用 shapeless 检测字段类型注解
how to use shapeless to detect field type annotation
我正在尝试使用 shapeless
收集在编译时具有特定注释的案例 class 的字段。我尝试尝试使用以下代码片段,但它没有按预期工作(不输出任何内容而不是打印 "i")。我怎样才能让它发挥作用?
import shapeless._
import shapeless.labelled._
final class searchable() extends scala.annotation.StaticAnnotation
final case class Foo(@searchable i: Int, s: String)
trait Boo[A] {
def print(a: A): Unit
}
sealed trait Boo0 {
implicit def hnil = new Boo[HNil] { def print(hnil: HNil): Unit = () }
implicit def hlist[K <: Symbol, V, RL <: HList](implicit b: Boo[RL]): Boo[FieldType[K, V] :: RL] =
new Boo[FieldType[K, V] :: RL] {
def print(a: FieldType[K, V] :: RL): Unit = {
b.print(a.tail)
}
}
}
sealed trait Boo1 extends Boo0 {
implicit def hlist1[K <: Symbol, V, RL <: HList](implicit annot: Annotation[searchable, K], witness: Witness.Aux[K], b: Boo[RL]): Boo[FieldType[K, V] :: RL] =
new Boo[FieldType[K, V] :: RL] {
def print(a: FieldType[K, V] :: RL): Unit = {
Console.println(witness.value.name)
b.print(a.tail)
}
}
}
object Boo extends Boo1 {
implicit def generics[A, HL <: HList](implicit iso: LabelledGeneric.Aux[A, HL], boo: Boo[HL]): Boo[A] =
new Boo[A] {
def print(a: A): Unit = {
boo.print(iso.to(a))
}
}
}
implicitly[Boo[Foo]].print(Foo(1, "2"))
查看 Annotation
的宏,它直接拒绝不是乘积或副积的类型
val annTreeOpts =
if (isProduct(tpe)) { ... }
else if (isCoproduct(tpe)) { ... }
else abort(s"$tpe is not case class like or the root of a sealed family of types")
这很不幸,因为在每个字段符号级别收集类型注释有时可能非常有用。
在同一文件中定义了另一种类型 class Annotations
,它实际上可以将字段上的特定注释收集到 HList
中。然而问题是现场信息完全丢失了。有一种笨拙的方法可以将事物组合在一起以服务于我的用例...
// A is our annotation
// B is our result type
// C is our case class with some fields annotated with A
def empty: B = ???
def concat(b1: B, b2: B): B = ???
def func(a: A, nm: String): B = ???
object Collector extends Poly2 {
implicit def some[K <: Symbol](implicit witness: Witness.Aux[K]) =
at[B, (K, Some[A])] { case (b, (_, a)) => concat(b, func(a.get, witness.value.name)) }
implicit def none[K <: Symbol] = at[B, (K, None.type)] { case (b, _) => b }
}
def collect[HL <: HList, RL <: HList, KL <: HList, ZL <: HList](implicit
iso: LabelledGeneric.Aux[C, HL]
, annot: Annotations.Aux[A, C, RL]
, keys: Keys.Aux[HL, KL]
, zip: Zip.Aux[KL :: RL :: HNil, ZL]
, leftFolder: LeftFolder.Aux[ZL, B, Collector.type, B]): B = {
zip(keys() :: annot() :: HNil).foldLeft(empty)(Collector)
}
我正在尝试使用 shapeless
收集在编译时具有特定注释的案例 class 的字段。我尝试尝试使用以下代码片段,但它没有按预期工作(不输出任何内容而不是打印 "i")。我怎样才能让它发挥作用?
import shapeless._
import shapeless.labelled._
final class searchable() extends scala.annotation.StaticAnnotation
final case class Foo(@searchable i: Int, s: String)
trait Boo[A] {
def print(a: A): Unit
}
sealed trait Boo0 {
implicit def hnil = new Boo[HNil] { def print(hnil: HNil): Unit = () }
implicit def hlist[K <: Symbol, V, RL <: HList](implicit b: Boo[RL]): Boo[FieldType[K, V] :: RL] =
new Boo[FieldType[K, V] :: RL] {
def print(a: FieldType[K, V] :: RL): Unit = {
b.print(a.tail)
}
}
}
sealed trait Boo1 extends Boo0 {
implicit def hlist1[K <: Symbol, V, RL <: HList](implicit annot: Annotation[searchable, K], witness: Witness.Aux[K], b: Boo[RL]): Boo[FieldType[K, V] :: RL] =
new Boo[FieldType[K, V] :: RL] {
def print(a: FieldType[K, V] :: RL): Unit = {
Console.println(witness.value.name)
b.print(a.tail)
}
}
}
object Boo extends Boo1 {
implicit def generics[A, HL <: HList](implicit iso: LabelledGeneric.Aux[A, HL], boo: Boo[HL]): Boo[A] =
new Boo[A] {
def print(a: A): Unit = {
boo.print(iso.to(a))
}
}
}
implicitly[Boo[Foo]].print(Foo(1, "2"))
查看 Annotation
的宏,它直接拒绝不是乘积或副积的类型
val annTreeOpts =
if (isProduct(tpe)) { ... }
else if (isCoproduct(tpe)) { ... }
else abort(s"$tpe is not case class like or the root of a sealed family of types")
这很不幸,因为在每个字段符号级别收集类型注释有时可能非常有用。
在同一文件中定义了另一种类型 class Annotations
,它实际上可以将字段上的特定注释收集到 HList
中。然而问题是现场信息完全丢失了。有一种笨拙的方法可以将事物组合在一起以服务于我的用例...
// A is our annotation
// B is our result type
// C is our case class with some fields annotated with A
def empty: B = ???
def concat(b1: B, b2: B): B = ???
def func(a: A, nm: String): B = ???
object Collector extends Poly2 {
implicit def some[K <: Symbol](implicit witness: Witness.Aux[K]) =
at[B, (K, Some[A])] { case (b, (_, a)) => concat(b, func(a.get, witness.value.name)) }
implicit def none[K <: Symbol] = at[B, (K, None.type)] { case (b, _) => b }
}
def collect[HL <: HList, RL <: HList, KL <: HList, ZL <: HList](implicit
iso: LabelledGeneric.Aux[C, HL]
, annot: Annotations.Aux[A, C, RL]
, keys: Keys.Aux[HL, KL]
, zip: Zip.Aux[KL :: RL :: HNil, ZL]
, leftFolder: LeftFolder.Aux[ZL, B, Collector.type, B]): B = {
zip(keys() :: annot() :: HNil).foldLeft(empty)(Collector)
}