适用于Scala和Java的类型安全的生成器库 [英] Type-safe Builder Library for Scala and Java

问题描述

以下是Scala中类型安全，流畅的构建器模式，如 http://www.tikalk.com/java/blog/type-safe-builder-scala-using-type-constraints .它类似于 Scala和Java的构建器库，但专门处理compile-时间生成器检查.如何从Java调用它?在给定"scala.Predef $$ eq $ colon $ eq"参数的情况下，可以使用Scala AND Java的干净API来完成此操作吗?

Below is a type-safe, fluid, builder pattern in Scala as described at http://www.tikalk.com/java/blog/type-safe-builder-scala-using-type-constraints. It's similar to Builder Library for Scala and Java, but deals specifically with compile-time builder checks. How can this called from Java? Can it be done with a clean 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]
}

推荐答案

与Scala版本相比，您应该能够从Java使用此API，并且会有一些额外的噪音.一些方便的字段将使事情变得安静:

You should be able to use this API from Java, with some extra noise compared to the Scala version. A few convenience fields will quiet things a bit:

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

Java客户端代码应该最终看起来像

The Java client code should end up looking like

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

build方法必须检查是否分配了每个属性，因此当您泛化为多个属性时，它会变得很嘈杂:

The build method has to check that every property is assigned, so it gets pretty noisy when you generalize to multiple properties:

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(), 
          //...
         );

在帮助器类中有一些静态委托(以及一些静态导入)，您应该可以将其简化为:

With some static delegates in a helper class (and some static imports), you should be able to get this down to something like:

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

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