斯卡拉方法=特质{...}的含义 [英] Scala method = trait { ... } meaning

问题描述

我试图同时学习Scala和Play框架。 Scala在我看来喜欢它有很多非常酷的想法，但我的一个挫折就是试图理解方法/函数/ lambdas /匿名函数/等的所有不同语法。

所以我有我的主要应用程序控制器如此：

 对象应用程序扩展控制器{
 def index = Action {
 Ok（views.html.index（Your new application is ready。））
} 
} 
  

这告诉我有一个singleton Application ，它有一个方法， index ，返回什么类型？我希望 index 的定义更像：

  def index （req：Request）：Result = {...} 
  

查看Play Framework的文档，就好像 Action 是一个特征，它将请求转换为结果，因为我很难理解这行代码是什么意思：

  def index =动作{...} 
  

我来自Java背景，所以我不知道这是什么意思？ （这种说法感觉像是在说'方法索引= [一些接口动作]，这对我来说没有意义;看起来好像有些美好的事情发生了，但这对我来说是神奇的，而我在我的代码中感到不自然）;）

解决方案

当你像对待一个函数一样调用一个对象时，调用应用。即：



  foo（bar）
  

被翻译成



  foo.apply（bar）
  index 中，您正在调用 Action   $ b> / code>对象就好像它是一个函数，这意味着你实际上调用了 Action.apply 。
 
 
 
返回类型 index 被忽略，因为编译器可以推断它是 Action.apply的返回类型（我猜的名字是 Unit ）。
 
I'm trying to learn Scala and the Play Framework at the same time.  Scala looks to me like it has a lot of really cool ideas, but one of my frustrations is trying to understand all of the different syntaxes for methods/functions/lambdas/anonymous functions/etc.

So I have my main application controller like so:
object Application extends Controller {
  def index = Action {
    Ok(views.html.index("Your new application is ready."))
  }
}
This tells me I have a singleton Application that has one method, index, that returns what type??  I was expecting index to have a definition more like:
def index(req: Request) : Result = { ... }
Looking at Play Framework's documentation, it looks as though Action is a trait, that transforms a request to a result, by I'm having a hard time understanding what this line is saying:
def index = Action { ... }
I come from a Java background, so I don't know what this is saying?  (this statement feels like it's saying "method index = [some interface Action]", which doesn't make sense to me; it seems something beautiful is happening, but it is magic to me, and I feel uneasy with magic in my code ;))
解决方案
When you invoke an object as if it were a function, that's translated into a call to apply. I.e.:
foo(bar)
is translated into 
foo.apply(bar)
So, inside index you are calling the Action object as if it were a function, which means you are actually calling Action.apply.

The return type of index is omitted because the compiler can infer it to be the return type of Action.apply (which I guess from the name is Unit).

                        
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