是否可以通过"this"?作为Scala中的隐式参数? [英] Is it possible to pass "this" as implicit parameter in Scala?

问题描述

假设我想用可以记录异常并继续执行的try-catch块包装可以引发异常的代码.像这样:

Suppose I want to wrap code that can throw exceptions with a try-catch block that logs the exception and continues. Something like:

loggingExceptions {
  // something dangerous
}

理想情况下，我想用于记录在调用对象上定义的Logger(如果有)(如果没有，则得到编译时错误).我很想定义这样的东西:

Ideally, I would like to use for logging the Logger defined on the calling object, if any (and if none, get a compile-time error). I'd love to define something like this:

def loggingExceptions[L <: { def logger: Logger }](work: => Unit)(implicit objectWithLogger: L): Unit = {
  try {
    work
  } catch {
    case t: Exception => objectWithLogger.logger.error(t.getMessage)
  }
}

其中objectWithLogger将以某种方式神奇地"在客户端代码中扩展为"this".这(或类似的东西)有可能吗?

where objectWithLogger would somehow "magically" expand to "this" in client code. Is this (or a similar thing) possible?

推荐答案

实际上，它可以随您所愿进行.其他答复者投降得太快.没有白旗！

It can in fact be done just as you want. The other answerers surrendered too quickly. No white flags!

package object foo {
  type HasLogger = { def logger: Logger }
  implicit def mkLog(x: HasLogger) = new {
    def loggingExceptions(body: => Unit): Unit =
      try body
      catch { case ex: Exception => println(ex) }
  }
}

package foo {
  case class Logger(name: String) { }

  // Doesn't compile:
  // class A {
  //   def f = this.loggingExceptions(println("hi"))
  // }
  // 1124.scala:14: error: value loggingExceptions is not a member of foo.A
  //         def f = this.loggingExceptions(println("hi"))
  //                      ^
  // one error found  

  // Does compile
  class B {
    def logger = Logger("B")
    def f = this.loggingExceptions(println("hi"))
    def g = this.loggingExceptions(throw new Exception)
  }
}

object Test {
  def main(args: Array[String]): Unit = {
    val b = new foo.B
    b.f
    b.g
  }
}

// output
//
// % scala Test
// hi
// java.lang.Exception

这篇关于是否可以通过"this"?作为Scala中的隐式参数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！