feature

Type Members

trait ByName[ByNameType] extends Serializable

A type class for convert between by-name type and normal by-value type.
A type class for convert between by-name type and normal by-value type.
Installation
```
libraryDependencies += "com.thoughtworks.feature" %% "byname" % "latest.release"
```
This ByName type class provide an extension method extract for ByName.=> types via implicit view, which can be import as follow:
```
import com.thoughtworks.feature.ByName.ops._
```
Author:

杨博 (Yang Bo) <[email protected]>

ByNameType
The by-name type
Note
When using this ByName type class, you should make sure the type parameter ByNameType is an abstract type, in case of Scala compiler bugs. You can use a trick similar to C++'s Pimpl Idiom to create opacity abstract types
import com.thoughtworks.feature.ByName.`=>` trait OpacityTypes { type IntByName implicit def typeClass: ByName.Aux[IntByName, Int] } val opacityTypes: OpacityTypes = new OpacityTypes { type IntByName = `=>`[Int] override def typeClass = ByName[IntByName] } import opacityTypes._
Now IntByName is an abstract type with underlying => Int type.
Given a by-name parameter of the return value of getInt(),
val getInt = stubFunction[Int] val boxedByName: IntByName = typeClass.make(getInt())
when getInt returns 42,
getInt.when.once returns 42
then the value of the the by-name parameter should be 42;
boxedByName.extract should be(42)
when getInt returns 144,
getInt.when.once returns 144
then the value of the the by-name parameter should be 144.
boxedByName.extract should be(144)

final class Caller[+A] extends AnyVal

An implicit value that points to the function caller.

Usage

libraryDependencies += "com.thoughtworks.feature" %% "caller" % "latest.release"

Getting the caller for logging or something

object Foo{
  def log()(implicit caller: Caller[Any]) = {
    println(caller.value)
  }
}
object Bar{
  Foo.log() // Bar
}

Restricting who you can be called from

class IKnowWhatImDoing
object Foo{
  def runDangerous()(implicit caller: Caller[IKnowWhatImDoing]) = {
    println(caller.value)
  }
}
object Bar {
  Foo.runDangerous() // compile error
}
object Bar2 extends IKnowWhatImDoing{
  Foo.runDangerous() // ok, prints Bar2
}

Getting calling class or classloader, e.g. for loading resources, without needing to worry about properly setting up and tearing down the Context ClassLoader

object Foo{
  def getResource(path: String)(implicit caller: Caller[_]) = {
    caller.value.getClass.getClassLoader.getResourceAsStream(path)
  }
}
object Bar{
  Foo.getResource("/thing/file.txt") // loads resource from `Bar`s classloader, always
}

Authors:

Li Haoyi

杨博 (Yang Bo) <[email protected]>

final class Constructor[F] extends AnyVal

An implicit value for dynamically creating classes and traits, especially dynamic mixins.
An implicit value for dynamically creating classes and traits, especially dynamic mixins.
Usage
```
libraryDependencies += "com.thoughtworks.feature" %% "constructor" % "latest.release"
```
```
trait A
trait B

def makeAWithB()(implicit constructor: Constructor[() => A with B]): A with B = {
  constructor.newInstance()
}

val ab: A with B = makeAWithB()
```
Motivation
This feature is useful for library authors. A library author may ask his user to create a trait type, then dynamically mix-in it with the features provided by the library.
Suppose you are creating a DSL that compiles to JavaScript.
You want your DSL is extensible. For example, the DSL users should be able to create custom binary operators.
With the help of Constructor.scala, you can put the boilerplate code into a private class BinaryOperator:
```
trait Ast

object Ast {

  class Literal(val n: Int) extends Ast {
    override final def compile(): String = n.compile()
  }

  private[Ast] abstract class BinaryOperator(leftHandSide: Ast, rightHandSide: Ast) extends Ast {
    protected def symbol: String
    override final def compile() = s"($leftHandSide $symbol $rightHandSide)"
  }

  def binaryOperator[T](leftHandSide: Ast, rightHandSide: Ast)(
    implicit constructor: Constructor[(Ast, Ast) => BinaryOperator with T]): BinaryOperator with T = {
    constructor.newInstance(leftHandSide, rightHandSide)
  }

}
```
The users only need a very simple implementation for their custom binary operators.
```
import Ast._

trait Plus {
  protected final def symbol = "+"
}

trait Minus {
  protected final def symbol = "-"
}

val myAst = binaryOperator[Plus](
  new Literal(1),
  binaryOperator[Minus](
    new Literal(3),
    new Literal(5)
  )
)

print(myAst.compile()) // Output: "(1 + (3 - 5))"
```
An alternative approach
There is another approach to integrate partial implementation from users: asking users to provide custom callback functions or type classes.
However, the callback functions or type classes approach will create additional object instances and additional references for each instance at run-time. On the other hand, the Constructor.scala approach create classes at compile-time and no additional run-time references. As a result, at run-time, Constructor.scala approach will consume less memory, and performs less indirect access on memory.
Author:

杨博 (Yang Bo) <[email protected]>
trait Demixin[ConjunctionType] extends AnyRef

A type class that converts a mix-in type to shapeless.HList.
A type class that converts a mix-in type to shapeless.HList.
Common imports
You may want to use Demixin with shapeless.HList.
```
import shapeless._
```
Examples:
1. The Demixin type class can be summoned from Demixin.apply method:
  class A; trait B; object C; val demixin = Demixin[A with B with C.type with String with Int]
  Out should be a shapeless.HList of each type components in the mix-in type ConjunctionType.
  "implicitly[demixin.Out =:= (A :: B :: C.type :: String :: Int :: HNil)]" should compile
  The elements in Out should keep the same order as type components in ConjunctionType.
  "implicitly[demixin.Out =:!= (String :: A :: B :: C.type :: Int :: HNil)]" should compile
2. Out of Demixin on scala.Any should be shapeless.HNil
  val demixin = Demixin[Any] "implicitly[demixin.Out =:= HNil]" should compile
3. Out of Demixin on non-mixed-in types other than scala.Any should be a shapeless.HList that contains only one element
  val demixin = Demixin[String] "implicitly[demixin.Out =:= (String :: HNil)]" should compile

trait Factory[Output] extends Serializable

A factory to create new instances, especially dynamic mix-ins.

Author:

杨博 (Yang Bo) <[email protected]>

Examples:

Given a trait that has abstract members.

trait Foo {
  val bar: Int
  var baz: Long
}

When creating a factory for the trait.

val factory = Factory[Foo]

Then the newInstance method of the factory should accept parameters according to abstract members.

val foo: Foo = factory.newInstance(bar = 1, baz = 2L)
foo.bar should be(1)
foo.baz should be(2L)

Given two traits that have no abstract member.
```
trait Foo
trait Bar
```
When creating a factory for mix-in type of the two types.
```
val factory = Factory[Foo with Bar]
```
Then the newInstance method of the factory should accept no parameters.
```
val fooBar: Foo with Bar = factory.newInstance()
fooBar should be(a[Foo])
fooBar should be(a[Bar])
```
Given a trait that contains an abstract method annotated as @inject.
```
import com.thoughtworks.feature.Factory.inject
trait Foo[A] {
  @inject def orderingA: Ordering[A]
}
```
When creating a factory for the trait
```
val factory = Factory[Foo[Int]]
```
Then the @inject method will be replaced to an implicit value.
```
val foo = factory.newInstance()
foo.orderingA should be(implicitly[Ordering[Int]])
```
It will not compile if no implicit value found. For example, Foo[Symbol] requires an implicit value of type Ordering[Symbol], which is not availble.
```
"Factory[Foo[Symbol]]" shouldNot compile
```

Note

However, if the nested type is an alias to another type outside of the type to create, then it is allowed

trait Outer {
  type Inner = String
  val inner: Option[Inner]
}
val outer: Outer = Factory[Outer].newInstance(inner = Some("my value"))
outer.inner should be(Some("my value"))

This Factory disallows creating types that has an abstract member whose type depends on nested types

trait Outer {
  trait Inner
  val inner: Option[Inner]
}
"Factory.newInstance[Outer](inner = None)" shouldNot typeCheck

@inject works on implicit abstract methods as well.

import com.thoughtworks.feature.Factory.inject
trait Foo[A] {
  @inject implicit def orderingA: Ordering[A]
}
Factory[Foo[Int]].newInstance().orderingA should be(implicitly[Ordering[Int]])

Factories may be nested

import com.thoughtworks.feature.Factory.inject
trait Outer {
  trait AbstractParameterApi
  type AbstractParameter <: AbstractParameterApi
  trait InnerApi {
    def foo: AbstractParameter
  }
  type Inner <: InnerApi
  @inject val innerFactory: Factory[Inner]
}
Factory[Outer]

trait Glb[Mixin] extends Serializable

A type class that converts a mix-in type to the greatest lower bound of the components of the mix-in.
A type class that converts a mix-in type to the greatest lower bound of the components of the mix-in.
This Glb type class provides an extension method glb via implicit view, which can be import as follow:
```
import com.thoughtworks.feature.Glb.ops._
```
Author:

杨博 (Yang Bo) <[email protected]>
Example:
1. Given a mix-in of two refinement components,
  type A = Option[Any] { def get: Immutable } type B = Option[Any] { def get: Iterable[String] } val ab: A with B = Some(List("cool"))
  when convert it to its greatest lower bound,
  val glbOfAB = toAllGlbOps(ab).glb
  Then the common method should return the greatest lower bound of each components's return type.
  val result: Immutable with Iterable[String] = glbOfAB.get result should be(List("cool"))
Note
This Glb type class is implemented via scala.reflect.api.Types.glb, which is similar to intersection operator in Dotty, except this Glb works for refinement type only.
,
The implicit conversion toAllGlbOps must be explicitly invoked, as a workaround of https://github.com/scala/bug/issues/10671
trait ImplicitApply[F] extends Serializable

A dependent type class that invokes F with implicit values as parameters.
A dependent type class that invokes F with implicit values as parameters.
Imports
```
import com.thoughtworks.feature.ImplicitApply.ops._
```
This will enable the implicitApply method for any functions
Author:

杨博 (Yang Bo) <[email protected]>

F
The function type to be implicitly invoked
Examples:
1. Given a function f that requires an Ordering[Int]
  val f = { x: Ordering[Int] => "OK" }
  Then f can implicitly apply as long as its parameter is implicitly available,
  f.implicitApply should be("OK")
2. Given a function f that requires an call-by-name Ordering[Int]
  def f0(x: => Ordering[Int]) = "OK" val f = f0 _
  Then f can implicitly apply as long as its parameter is implicitly available,
  f.implicitApply should be("OK")
Note
You can optionally add an implicit modifier on the function parameter.
val f = { implicit x: Ordering[Int] => "OK" } f.implicitApply should be("OK")
It is very useful when you create a curried function.
def g[A] = { (i: A, j: A) => implicit x: Ordering[A] => import x._ if (i > j) { s"$i is greater than $j" } else { s"$i is not greater than $j" } } g(1, 2).implicitApply should be("1 is not greater than 2")
trait Mixin[L <: HList] extends AnyRef

A type class that converts a shapeless.HList to a mix-in type.
A type class that converts a shapeless.HList to a mix-in type.
Common imports
You may want to use Mixin with shapeless.HList.
```
import shapeless._
```
Example:
1. Out of Mixin is a minx-in type that consists of each types in L
  val mixin = Mixin[Int :: Nil.type :: String :: HNil] "implicitly[mixin.Out =:= (Int with Nil.type with String)]" should compile

trait PartialApply[F, ParameterName <: String with Singleton] extends Serializable

A dependent type class that bind the specific parameter of ParameterName to F

Imports

import com.thoughtworks.feature.PartialApply.ops._

This will enable the partialApply method for any functions

Author:

杨博 (Yang Bo) <[email protected]>

F: The function type to be partially apply

Examples:

Given a function with three parameters.

val f = { (v1: Int, v2: Int, v3: Int) => (v1 + v2) * v3 }

When partially applying the second parameter.

val partiallyApplied = f.partialApply(v2 = 2)

And applying the rest parameters.

val result = partiallyApplied(v3 = 3, v1 = 1)

Then the result should be the same as applying at once.

result should be(f(1, 2, 3))

A function with refined parameters can partially apply.

val f: ((Int, Double, String) => String) { def apply(i: Int, d: Double, s: String): String } = { (i, d, s) =>
  (i * d) + s
}
f.partialApply(s = "seconds").apply(i = 60, d = 1.125) should be(f(s = "seconds", i = 60, d = 1.125))

Partial applying can be chained.

val f = { (v1: Int, v2: Int, v3: Int) => (v1 + v2) * v3 }
f.partialApply(v2 = 2).partialApply(v3 = 3).partialApply(v1 = 1).apply() should be(f(1, 2, 3))

Function objects can partially apply.

object f extends ((Int, Double, String) => String) {
  def apply(i: Int, d: Double, s: String): String = {
    (i * d) + s
  }
}
f.partialApply(s = "seconds").apply(i = 60, d = 1.125) should be(f(s = "seconds", i = 60, d = 1.125))

Case class companion can partially apply.

case class MyCaseClass(i: Int, d: Double, s: String)
MyCaseClass.partialApply(s = "seconds").apply(i = 60, d = 1.125) should be(MyCaseClass(s = "seconds", i = 60, d = 1.125))

Call-by-name functions can partially apply.

def foo(v1: => String, v2: Int) = v1 + v2
val callByNameFunction = foo _
PartialApply.materialize[callByNameFunction.type, "v1"].apply(callByNameFunction, "1").apply(v2 = 2) should be(foo(v1 = "1", v2 = 2))

trait SelfType[A] extends AnyRef

A type class that extracts the self-type of A.

Examples:

Given a compound type

trait MySelfType1
trait MyTrait1 { this: MySelfType1 => }
trait MyTrait2
trait MySelfType3
trait MyTrait3 { this: MySelfType3 => }
type MyCompoundType = MyTrait1 with MyTrait2 with MyTrait3 {
  type MyRefinement = Int
}

Then the self type should be a compound type of each mix-in part

val selfType = SelfType[MyCompoundType]
"implicitly[selfType.Out =:= (MySelfType1 with MySelfType3 with MyTrait1 with MyTrait2 with MyTrait3)]" should compile

And the self type should not contain the refinement statements

"implicitly[selfType.Out <:< { type MyRefinement = Int }]" shouldNot typeCheck

Given a trait with an explicit self-type declaration

trait MySelfType
trait MyTrait { this: MySelfType => }

Then the self type should be itself

val selfType = SelfType[MyTrait]
"implicitly[selfType.Out =:= (MySelfType with MyTrait)]" should compile

Given a trait without an explicit self-type declaration

trait MyTrait

Then the self type should be itself

val selfType = SelfType[MyTrait]
"implicitly[selfType.Out =:= MyTrait]" should compile

trait Structural[Mixin] extends Serializable

A type class that converts a class type to a refinement type

This Structural type class provides an extension method structuralize via implicit view, which can be import as follow:

import com.thoughtworks.feature.Structural.ops._

Examples:

Given a class that contains abstract types:

trait Container extends Iterable[String] {
  trait InnerApi
  type Inner <: InnerApi
  def inner: Inner = ???
  type Self0 >: this.type
  def self: Self0 = this
}
val container: Container = new Container { def iterator = Iterator.empty }

When converting it to a structural type

import scala.language.higherKinds
val myStruct = container.structuralize

Then methods on the converted struct should be able to access via reflective call

import scala.language.reflectiveCalls
myStruct.self should be(myStruct)

Given a String

val myString: String = "foo"

When converting it to a structural type

val myStruct = myString.structuralize

Then methods on the converted struct should be able to access via reflective call

import scala.language.reflectiveCalls
myStruct.startsWith("f") should be(true)

However, the struct is not a String

"struct: String" shouldNot typeCheck

final class The[Widen, Narrow <: Widen] extends AnyVal

A helper that summons dependent type class Widen.
A helper that summons dependent type class Widen.
Note
The can be used as an alternative to implicitly for dependent type classes.
val narrowed: Int <:< Int = The[Int <:< Any].value
See also
https://github.com/milessabin/shapeless/pull/695 for discussion about the motivation of The.
class Untyper[Universe <: Singleton with Universe] extends AnyRef

A utility to convert Type to Tree.
A utility to convert Type to Tree.

Author:

杨博 (Yang Bo) <[email protected]>

Note
The primary intent of Untyper class is for some macro libraries in this feature.scala project, although it may also useful for other projects.

Value Members

object ByName extends Serializable
object Caller
object Constructor
object Demixin
object Factory extends Serializable
object Glb extends Serializable
object ImplicitApply extends Serializable
object Mixin extends LowPriorityMixin
object PartialApply extends Serializable
object SelfType
object Structural extends Serializable
object The
package mixins

package feature

Type Members

trait ByName[ByNameType] extends Serializable

Installation

Author:

final class Caller[+A] extends AnyVal

Usage

Getting the caller for logging or something

Restricting who you can be called from

Getting calling class or classloader, e.g. for loading resources, without needing to worry about properly setting up and tearing down the Context ClassLoader

Authors:

final class Constructor[F] extends AnyVal

Usage

Motivation

An alternative approach

Author:

trait Demixin[ConjunctionType] extends AnyRef

Common imports

trait Factory[Output] extends Serializable

Author:

trait Glb[Mixin] extends Serializable

Author:

trait ImplicitApply[F] extends Serializable

Imports

Author:

trait Mixin[L <: HList] extends AnyRef

Common imports

trait PartialApply[F, ParameterName <: String with Singleton] extends Serializable

Imports

Author:

trait SelfType[A] extends AnyRef

trait Structural[Mixin] extends Serializable

final class The[Widen, Narrow <: Widen] extends AnyVal

class Untyper[Universe <: Singleton with Universe] extends AnyRef

Author:

Value Members

object ByName extends Serializable

object Caller

object Constructor

object Demixin

object Factory extends Serializable

object Glb extends Serializable

object ImplicitApply extends Serializable

object Mixin extends LowPriorityMixin

object PartialApply extends Serializable

object SelfType

object Structural extends Serializable

object The

package mixins

Ungrouped