具有类型参数限制的Scala通用类的条件方法 [英] Conditional methods of Scala generic classes with restrictions for type parameters

问题描述

我相信泛型类只有在其类型参数符合某些附加限制的情况下才可以使它的一种方法可用，例如(当场即兴使用的语法):

I believe that a generic class may make one of its methods available only assuming that its type parameters conform to some additional restrictions, something like (syntax improvised on the spot):

trait Col[T] extends Traversable[T] {
    def sum[T<:Int] :T = (0/:this)(_+_)
}

我想我可以使用隐式参数作为证据...对此是否有语言功能?

I guess I could use implicit parameters as evidence... Is there a language feature for this?

推荐答案

在这种情况下，您只能使用隐式参数，因为类型是在方法调用之前确定的.

In this case you can only use an implicit parameter, as the type gets determined before the method call.

trait Col[T] extends Traversable[T] {
  def sum(implicit num: Numeric[T]) :T = ???
}

如果要调用的方法将被参数化，则可以使用上下文绑定，它只是绑定到类型参数的隐式参数的语法糖:

If the method you are calling would be parameterized, you could use context bounds, which are just syntactic sugar for the implicit parameter bound to the type parameter:

def foo[A](implicit ev: Something[A]) = ???

等同于

def foo[A : Something] = ???

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