隐式、粉刺图案等

发布于 2024-10-18 20:08:35 字数 311 浏览 2 评论 0原文

假设我有这些类：

case class A()
case class B()
case class C(a: A, b: B)

和这些变量：

val a = A()
val b = B()

有没有办法隐式获取 C 的实例，而不需要创建 a 和 b隐式值？即，如果我有一个需要 C 的方法：

def foo(c: C)

原文

Let's say that I have these classes:

case class A()
case class B()
case class C(a: A, b: B)

and these variables:

val a = A()
val b = B()

Is there a way to get an instance of C implicitly and without making a and b implicit vals? I.e. if I have a method expecting a C:

def foo(c: C)

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

狂之美人 2024-10-25 20:08:35

case class A 表示法已被弃用。您必须使用 case class A()，否则将 A 分配给 val a 将导致 a 引用到在场景后面生成的案例类 A 的伴生对象。

据我了解，您希望 a 引用案例类的实例，而不是伴随对象。

如果是这样，您所要求的是可能的 - a 和 b 不必是隐式的，但您必须在作用域中添加一个新的隐式方法：

implicit def obtainC = new C(a, b)

然后，您必须将 implicit 修饰符添加到方法 foo 中的 c：

def foo(implicit c: C)

完成会话：

scala> case class A()
defined class A

scala> case class B()
defined class B

scala> case class C(a: A, b: B)
defined class C

scala> val a = A()
a: A = A()

scala> val b = B()
b: B = B()

scala> implicit def obtainC = new C(a, b)
obtainC: C

scala> def foo(implicit c: C) = {}
foo: (implicit c: C)Unit

scala> foo

The case class A notation was deprecated. You have to use case class A(), otherwise assigning A to the val a will result in a referring to the companion object of the case class A which is generated behind the scene.

It's my understanding you wanted a to refer to the instance of the case class, not the companion object.

If so, what you're asking is possible - a and b don't have to be implicit, but you do have to add a new implicit method into the scope:

implicit def obtainC = new C(a, b)

Then, you have to put the implicit modifier to c in the method foo:

def foo(implicit c: C)

Complete session:

scala> case class A()
defined class A

scala> case class B()
defined class B

scala> case class C(a: A, b: B)
defined class C

scala> val a = A()
a: A = A()

scala> val b = B()
b: B = B()

scala> implicit def obtainC = new C(a, b)
obtainC: C

scala> def foo(implicit c: C) = {}
foo: (implicit c: C)Unit

scala> foo

回复收藏 0 原文

~没有更多了~