scala - 未应用旋转模板默认参数值

Question

我有一个 Play 2.5 模板，它从以下声明开始：

@(title: String)(content: Html)(menu:Html = HtmlFormat.empty)(implicit request:Request[AnyContent])

所以第二个参数被声明为具有默认值。

现在在控制器中我有这个动作生成器：

def document(title:String) = Action.async{implicit request =>
    documentService.findByTitle(title).map{
      case Some(d) => Ok(views.html.document(d))
      case None => Ok(main("No document found")(content = Html("There is no such document")))
    }
  }

所以我没有将menu参数的值传递给模板调用，我希望它能够按照默认参数值语义进行编译和工作，但是我收到了这个编译错误：

[error] D:\Projects\feed\app\controllers\MainController.scala:28: missing arguments for method apply in class main; 
[error] follow this method with `_' if you want to treat it as a partially applied function 
[error] case None => Ok(main("No document found")(content = Html("There is no such document"))) 
[error]                                          ^ 
[error] one error found 
[error] (compile:compileIncremental) Compilation failed

你能解释一下这里有什么问题吗？

Answer 1

再添加一对括号。

Ok(main("No document found")(content = Html("There is no such document")()))

没有最后一个括号 - 它只是一个等待另一个参数的函数。您可以检查您调用的函数的类型。我将展示我的示例：

def foo(a: Int = 3) = 41

val one = foo //wan't compile
val two: (Int) => Int = foo
val three: Int = foo()