scala：用重载来修饰我的库
有什么想法为什么以下不起作用？
implicit def listExtensions[A](xs : List[A]) = new ListExtensions(xs)
class ListExtensions[A](xs : List[A])
{
def foreach[B](f: (A, Int) => B)
{
var i = 0;
for (el <- xs)
{
f(el, i);
i += 1;
}
}
}
var a = List(1, 2, 3);
a foreach { (el, i) => println(el, i) };
当我使用 fsc 2.8.1 编译此文件时，出现以下错误：“参数数量错误；预期 = 1: a foreach { (el, i) => println(el, i) };”。我是否做错了什么，或者根本没有办法通过“拉皮条我的库”技巧来添加重载方法？
PS 我不知道如何实现 foreach 的 iterate-with-current-index 风格（我知道 zipWithIndex 方法），而是想知道重载和隐式转换如何一起发挥作用。
Any ideas why doesn't the following work?
implicit def listExtensions[A](xs : List[A]) = new ListExtensions(xs)
class ListExtensions[A](xs : List[A])
{
def foreach[B](f: (A, Int) => B)
{
var i = 0;
for (el <- xs)
{
f(el, i);
i += 1;
}
}
}
var a = List(1, 2, 3);
a foreach { (el, i) => println(el, i) };
When I compile this with fsc 2.8.1, I get the following error: "wrong number of parameters; expected = 1: a foreach { (el, i) => println(el, i) };". Am I doing something wrong or there simply ain't a way to add an overloaded method by the means of "pimp my library" trick?
P.S. I wonder not about implementing the iterate-with-current-index flavor of foreach (I'm aware of zipWithIndex method), but rather about how overloading and implicit conversions play together.
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编译器永远不会尝试使用隐式转换，因为 List 上已经有一个 foreach 方法。更具体地说，Scala 语言规范 (http://www.scala-lang.org/docu/files/ScalaReference.pdf) 的第 7.3 节指出，隐式转换应用于两种情况，第二种情况与示例相关：
顺便说一句，您可以使用 zipWithIndex 方法完成带有索引的 foreach。
The compiler never attempts to use the implicit conversion because there's already a foreach method on List. More specifically, section 7.3 of the Scala Language Specification (http://www.scala-lang.org/docu/files/ScalaReference.pdf) states that an implicit conversion is applied in two cases, with the second case relevant to the example:
As an aside, you can accomplish a foreach with an index by using the zipWithIndex method.
仅当您尝试使用源类型上不存在的方法时，隐式转换才会启动。
在这种情况下，List有一个foreach方法，因此不会考虑转换。但是您会因与预期签名不匹配而收到错误。
Implicit conversion will only kick in when you attempt to use a method that doesn't exist on the source type.
In this case, List has a foreach method, so no conversion will be considered. But you will get an error for not matching the expected signature.
或者，将名称更改为 foreachWithIndex
Or, change the name to foreachWithIndex