[英]Scala Generics - T has method restrictions
I am new with scala generics, I have read multiple articles about views, type bound/context bound. 我是scala泛型的新手,我已经阅读了多篇有关视图,类型绑定/上下文绑定的文章。 When I have tried to implement my class, I was really confused.
当我尝试实现我的课程时,我真的很困惑。
My question is, let's say I have a template class MyClass[T]{} . 我的问题是,假设我有一个模板类MyClass [T] {} 。 I want that T must have some methods for example :
我希望T必须具有一些方法,例如:
def func1(t:T):T
def func2(t:T):Boolean
def func3(t:T):Unit
Note: classes that will use MyClass are not T therefore I cannot use :< or :> 注意:将使用MyClass的类不是T,因此我不能使用:<或:>
I have read about Ordered and Ordering that have implicit function, but I still cannot figure out how to implement it. 我已经阅读了有关具有隐式功能的Ordered和Ordering的信息,但是我仍然无法弄清楚如何实现它。
Thanks for helpers 谢谢帮手
You can do that with typeclasses. 您可以使用typeclass做到这一点。 Create a
trait
, that contains the methods you need and for every type that should be supported create an implicit instance: 创建一个
trait
,其中包含所需的方法,并为应支持的每种类型创建一个隐式实例:
trait MyTypeClass[T] {
def func1(t:T):T
def func2(t:T):Boolean
def func3(t:T):Unit
}
implicit object MyTypeClassInt extends MyTypeClass[Int] {
def func1(t:Int) = t + 2
def func2(t:Int) = t > 4
def func3(t:Int) = println(s"t is: $t")
}
Now if you add a context bound to the type parameter in your class, it can only be instantiated, when an instance for the given type is in scope. 现在,如果您在类中添加了绑定到类型参数的上下文,则只有当给定类型的实例在范围内时,才能实例化该上下文。
class MyClass[A : MyTypeClass](a: A)
scala> new MyClass(2)
res0: MyClass[Int] = MyClass@47825164
scala> new MyClass("")
<console>:11: error: could not find implicit value for evidence parameter of type MyTypeClass[String]
new MyClass("")**
You can access the instance in your class by calling implicitly[MyTypeClass[A]]
. 您可以通过
implicitly[MyTypeClass[A]]
调用implicitly[MyTypeClass[A]]
来访问类中的实例。 Alternatively you can do one of the following things: 或者,您可以执行以下任一操作:
1.) Instead of using a context bound add an implicit parameter to your class: 1.)代替使用上下文绑定,将隐式参数添加到您的类中:
class MyClass[A](a: A)(implicit ev: MyTypeClass[A])
2.) Add a companion for your typeclass, that has an apply method, that implicitly retrieves the instance and returns it: 2.)为您的类型类添加一个同伴,该同伴具有一个apply方法,该同伴隐式地检索该实例并将其返回:
object MyTypeClass {
def apply[A](implicit ev: MyTypeClass[A]) = ev
}
and use it in your class like this: 并在您的班级中像这样使用它:
MyTypeClass[A].func1(a)
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