Scala DSL、对象和中缀表示法

发布于 2024-09-02 01:06:44 字数 243 浏览 4 评论 0原文

在 Scala 中，如果我想实现 DSL，有没有办法执行以下操作：

我有一个名为“Draw”的对象，其中包含函数 def draw(d:Drawable)

我该如何制作这样我就可以导入对象并在对象外部调用它，例如：

draw ball

如果球扩展了可绘制特征？问题是我想以一种中缀表示法使用绘制，但我不想通过表示它正在实现类/对象来限定函数绘制。

原文

in Scala, if I want to implement a DSL, is there a way to do the following:

I have an Object called "Draw" which contains the function def draw(d:Drawable)

how can I make it so that I can import the Object and call it outside the object like:

draw ball

if ball extends the Drawable trait? The problem is that I want to use draw in a kind of infix notation, but I dont want to qualify the function draw by denoting it's implementing class/object.

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紫﹏色ふ单纯 2024-09-09 01:06:44

你做不到。除了四个前缀运算符之外，在任何运算符表示法中，第一个标记都表示对象。

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杀手六號 2024-09-09 01:06:44

我很快就尝试了一下，但使用一个对象完全可以使其工作。在那里，我必须使用绘制（球）而不是绘制球，如您所愿：


Welcome to Scala version 2.8.0.RC2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_20).

标量>特质 Drawable{def doSomething}
定义的特征 Drawable

 scala>对象绘制 {

        def draw(d:Drawable) = d.doSomething
     }
定义模块Draw

 scala> val ball = new Drawable{def doSomething = println("做球")}
球：java.lang.Object with Drawable = $anon$1@3a4ba4d6

 scala>导入绘图._
导入Draw._scala

 >抽球
:11: 错误: 对象 Draw 中缺少方法绘制的参数；
如果您想将其视为部分应用函数，请在此方法后面加上“_”
       抽球
       ^

标量>画（球）
做球

然而，通过将 Draw 定义为一个类，它确实起作用了：


scala> trait Drawable{def doSomething: Unit}
defined trait Drawable

标量>绘图类 {

        def draw(d:Drawable) = d.doSomething
     }
定义类Draw

 scala>

标量> val ball = new Drawable{def doSomething = println("做球")}
球：java.lang.Object with Drawable = $anon$1@36a06816

 scala> val d = 新抽奖
d: Draw = Draw@7194f467

 scala> d 画球
做球

我不完全确定为什么这与对象的工作方式不同，可能是一个错误，或者可能是指定的行为。不过我现在没有时间去查。

I quickly tried it out, but could quite make it work using an object. There I had to use draw(ball) instead of draw ball, as you wanted:


Welcome to Scala version 2.8.0.RC2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_20).

scala> trait Drawable{def doSomething}
defined trait Drawable

scala> object Draw {

        def draw(d:Drawable) = d.doSomething
     }
defined module Draw

scala> val ball = new Drawable{def doSomething = println("doing ball")}
ball: java.lang.Object with Drawable = $anon$1@3a4ba4d6

scala> import Draw._
import Draw._

scala> draw ball
:11: error: missing arguments for method draw in object Draw;
follow this method with `_' if you want to treat it as a partially applied function
       draw ball
       ^

scala> draw(ball)
doing ball

However by defining Draw as a class, it did work:


scala> trait Drawable{def doSomething: Unit}
defined trait Drawable

scala> class Draw {

        def draw(d:Drawable) = d.doSomething
     }
defined class Draw

scala> 

scala> val ball = new Drawable{def doSomething = println("doing ball")}
ball: java.lang.Object with Drawable = $anon$1@36a06816

scala> val d = new Draw
d: Draw = Draw@7194f467

scala> d draw ball
doing ball

I'm not completely sure why this doesn't work the same way with an object, might be a bug or perhaps that's specified behaviour. However I didn't have the time to look it up at the moment.

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