一个问题本质上类似于
subtle differences between val and def.我想知道成员单例对象之间的语义差异是什么:
class Text { ... object Whitespace { def unapply(s :String) = if (s.forall(_.isWhitespace)) Some(s) else None } }
和
class Text { ... val Whitespace = new { def unapply(s :String) = if (s.forall(_.isWhitespace)) Some(s) else None } }
我知道两者都转换为字节码,但我能用代码中的一个转换为另一个吗?
解决方法
您需要更加努力地覆盖成员对象.
apm@mara:~/tmp$skala Welcome to Scala version 2.11.0-20130622-103744-990c2b024a (OpenJDK 64-Bit Server VM,Java 1.7.0_21). Type in expressions to have them evaluated. Type :help for more information. scala> class Foo1 { val foo = () => 1 } defined class Foo1 scala> class Bar1 extends Foo1 { override val foo = () => 2 } defined class Bar1 scala> class Foo2 { object foo { def apply() = 3 } } defined class Foo2 scala> class Bar2 extends Foo2 { override object foo { def apply() = 4 }} <console>:8: error: overriding object foo in class Foo2; object foo cannot override final member class Bar2 extends Foo2 { override object foo { def apply() = 4 }} ^ scala> :q apm@mara:~/tmp$skala -Yoverride-objects Welcome to Scala version 2.11.0-20130622-103744-990c2b024a (OpenJDK 64-Bit Server VM,Java 1.7.0_21). Type in expressions to have them evaluated. Type :help for more information. scala> class Foo2 { object foo { def apply() = 3 } } defined class Foo2 scala> class Bar2 extends Foo2 { override object foo { def apply() = 4 }} defined class Bar2 scala> new Bar2 res0: Bar2 = Bar2@508c825 scala> .foo() res1: Int = 4 scala> :q
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