用对象覆盖方法

为什么可以用object覆盖空括号方法？用对象覆盖方法

trait A { 
    def meth = {} 
    def meth_p() = {} 
} 

class B extends A { 
    object meth_p 
} // compiles

压倒一切的不带括号的方法不编译：

class B1 extends A { 
    object meth 
} // does not compile

无论做任何下列组合工作的（不含override修改）：

class BX extends A { 
    // of course, each declaration should get its own class 
    def meth = {} 
    def meth_p() = {} 
    def meth() = {} 
    def meth_p = {} 
    val meth = {} 
    val meth_p = {} 
    // ... 
}

这是记载和有用的行为？由于意外覆盖，我遇到了一个非常微妙的错误。

来源

2011-09-28 Debilski

这确实看起来像一个错误。如果你这样做，反过来就会变得更加怪异。

class A { 
    object m { override def toString = "object m" } 
} 

class B extends A { 
    def m() = "def m" 
} 

scala> (new A).m 
res0: object A#m = object m 

scala> (new A).m() // doesn't compile 

scala> (new B).m 
<console>:10: error: ambiguous reference to overloaded definition, 
both method m in class B of type()java.lang.String 
and object m in class A of type object B#m 
match expected type ? 
       (new B).m 
        ^
scala> (new B).m() 
java.lang.VerifyError: class B overrides final method m.()LA$m$; 
     at java.lang.ClassLoader.defineClass1(Native Method) 
     at java.lang.ClassLoader.defineClassCond(Unknown Source) 
     at java.lang.ClassLoader.defineClass(Unknown Source) 
     at java.lang.ClassLoader.defineClass(Unknown Source) 
     at scala.tools.nsc.interpreter.AbstractFileClassLoader.findClass(AbstractFileClassLoader.scala:52) 
     at java.lang.ClassLoader.loadClass(Unknown Source) 
     at scala.tools.nsc.interpreter.AbstractFileClassLoader.scala$tools$nsc$util$ScalaClassLoader$$super$loadClass(AbstractFileClassLoader.scala:17) 
     at scala.tools.nsc.util.ScalaClassLoader$class.loadClass(ScalaClassLoader.scala:50) 
     at scala.tools.nsc.interpreter.AbstractFileClassLoader.loadClass(AbstractFileClassLoader.scala:17) 
     at java.lang.ClassLoader.loadClass(Unknown Source) 
     at .<init>(<console>:10) 
     at .<clinit>(<console>) 
     at .<init>(<console>:11) 
     at .<clinit>(<console>) 
     at $print(<console>) 
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
     at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) 
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) 
     at java.lang.reflect.Method.invoke(Unknown Source) 
     at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704) 
     at scala.tools.nsc.interpreter.IMain$Request$$anonfun$14.apply(IMain.scala:920) 
     at scala.tools.nsc.interpreter.Line$$anonfun$1.apply$mcV$sp(Line.scala:43) 
     at scala.tools.nsc.io.package$$anon$2.run(package.scala:25) 
     at java.lang.Thread.run(Unknown Source)

来源

2011-09-28 14:51:15 agilesteel

是的，这看起来更像是一个错误。 – Debilski

https://issues.scala-lang.org/browse/SI-5429 – soc

用对象覆盖方法

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