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Builder sample library for Scala and Java

The following is a safe, fluid type builder in Scala, as described at http://www.tikalk.com/java/blog/type-safe-builder-scala-using-type-constraints . It is similar to the Builder library for Scala and Java , but specifically deals with checking the compiler-time builder. What is it called with Java? Can this be done using a pure API for Scala AND Java, given the scala.Predef $$ eq $ colon $ eq parameters?

sealed trait TBoolean
sealed trait TTrue extends TBoolean
sealed trait TFalse extends TBoolean

class Builder[HasProperty <: TBoolean] private(i: Int) {
  protected def this() = this(-1)
  def withProperty(i: Int)(implicit ev: HasProperty =:= TFalse) = new Builder[TTrue](i)
  def build(implicit ev: HasProperty =:= TTrue) = println(i)
}

//javap output
    public class Builder extends java.lang.Object implements scala.ScalaObject{
    public Builder withProperty(int, scala.Predef$$eq$colon$eq); //How is this called from Java?
    public void build(scala.Predef$$eq$colon$eq);
    public Builder();
}
object Builder {
  def apply() = new Builder[TFalse]
}
+4
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2 answers

API Java Scala. :

object Builder {
   def apply() = new Builder[TFalse]
   val unassigned = =:=.tpEquals[TFalse]
   val assigned = =:=.tpEquals[TTrue] 
}

Java :

Builder$.MODULE$.apply()
   .withProperty(10, Builder$.MODULE$.unassigned())
   .build(Builder$.MODULE$.assigned());

build , , :

Builder$.MODULE$.apply()
   .withProp1(10, Builder$.MODULE$.unassigned())
   .withProp2(20, Builder$.MODULE$.unassigned())
   .withProp3(30, Builder$.MODULE$.unassigned())
   // ...
   .build(Builder$.MODULE$.assigned(), 
          Builder$.MODULE$.assigned(), 
          Builder$.MODULE$.assigned(), 
          //...
         );

- ( ) :

createBuilder()
   .withProp1(10, unassigned())
   .withProp2(20, unassigned())
   .build(assigned(), assigned());
+6

, Aaron ittayd... API Scala Java:

import annotation.bridge

sealed trait TBoolean
sealed trait TTrue extends TBoolean
sealed trait TFalse extends TBoolean

class Builder[HasProperty <: TBoolean] private(i: Int) {
  protected def this() = this(-1)

  def withProperty(i: Int)(implicit ev: HasProperty =:= TFalse) = new Builder[TTrue](i)
  def build(implicit ev: HasProperty =:= TTrue):Int = i
  @bridge def withProperty(i: Int) = new Builder[TTrue](i)
  @bridge def build = build(null)
}

object Builder {
  def apply() = new Builder[TFalse]
  val unassigned = =:=.tpEquals[TFalse]
  val assigned = =:=.tpEquals[TTrue]
}

Scala ( Safe):

val v = Builder().withProperty(2).build

Java ( , ):

int i = Builder$.MODULE$.apply()
        .withProperty(5, Builder$.MODULE$.unassigned())
         .build(Builder$.MODULE$.assigned());

Java Usage II ( , , @Bridge):

static Builder createBuilder() {
  return Builder$.MODULE$.apply();
}
...
int j = createBuilder().withProperty(7).build();
+3

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