Scala 类值参数的类型成员的类型不匹配
为什么使用绑定到类值参数的类型成员会产生“类型不匹配”错误?例如:Scala 类值参数的类型成员的类型不匹配,scala,type-members,Scala,Type Members,为什么使用绑定到类值参数的类型成员会产生“类型不匹配”错误?例如: scala> class A { type t } defined class A scala> class B(val a: A) defined class B scala> val aInt = new A { type t = Int } aInt: A{type t = Int} = $anon$1@6ccc7368 scala> val b = new B(aInt) b: B = B@
scala> class A { type t }
defined class A
scala> class B(val a: A)
defined class B
scala> val aInt = new A { type t = Int }
aInt: A{type t = Int} = $anon$1@6ccc7368
scala> val b = new B(aInt)
b: B = B@834518
scala> val i: b.a.t = 1
<console>:11: error: type mismatch;
found : Int(1)
required: b.a.t
val i: b.a.t = 1
^
这种行为的原因是什么?似乎我已经明白发生了什么。在类
B
的示例中,值a
转换为类型a
,该类型t
没有确定的值。在抽象类C
的示例中,实例C
用aInt
覆盖a
的值,该值具有t
的具体类型。换句话说,c
不是c
的实例:它是其匿名子类的实例
如果我将说明c
类型的示例明确更改为c
,则得到与第一种情况相同的错误:
scala> class A { type t }
defined class A
scala> val aInt = new A { type t = Int }
aInt: A{type t = Int} = $anon$1@3b8590c5
scala> abstract class C { val a: A }
defined class C
scala> val c: C = new C { val a = aInt }
c: C = $anon$1@5f14a3c6
scala> val i: c.a.t = 1
<console>:11: error: type mismatch;
found : Int(1)
required: c.a.t
val i: c.a.t = 1
^
scala>class A{type t}
定义的A类
scala>val aInt=newa{type t=Int}
aInt:A{type t=Int}=$anon$1@3b8590c5
scala>抽象类C{val a:a}
定义的C类
scala>valc:c=newc{vala=aInt}
c:c=$anon$1@5f14a3c6
scala>vali:c.a.t=1
:11:错误:类型不匹配;
发现:Int(1)
必填项:c.a.t
val i:c.a.t=1
^
scala> class A { type t }
defined class A
scala> val aInt = new A { type t = Int }
aInt: A{type t = Int} = $anon$1@3b8590c5
scala> abstract class C { val a: A }
defined class C
scala> val c: C = new C { val a = aInt }
c: C = $anon$1@5f14a3c6
scala> val i: c.a.t = 1
<console>:11: error: type mismatch;
found : Int(1)
required: c.a.t
val i: c.a.t = 1
^