Scala隐式类和继承

Question

假设我想向String类添加一些方法。但是应该应用的具体隐式类在运行时已知（策略模式）。比方说，我们有

trait StringExtensions { 
    def doSth(str: String): String 
} 

class Strategy1 extends StringExtensions { 
    override def doSth(str: String): String = "a" 
} 

class Strategy2 extends StringExtensions { 
    override def doSth(str: String): String = "b" 
} 

现在我的客户端代码如下所示：

def someMethod(strategy: StringExtensions) : String{ 
    val name = "Pawel" 
    return strategy.doSth(name) 
} 
... 
String ret = someMethod(new Strategy1()) 

，但我想有这样的代码：

def someMethod(strategy: StringExtensions) : String{ 
    val name = "Pawel" 
    return name.doSth() // Here is the tricky line 
} 
... 
String ret = someMethod(new Strategy1()) 

我打得有点与implicits但正值当继承这个用例我找不到合适的解决方案，有什么帮助？

Answer 1

我不确定你应该真的使用这样的含义，但也许在某些DSL这可能是一个有效的用例。

class StringExtensions(str: String, strategy: StringExtensionsStrategy) { 
    def doSth() = strategy.doSth(str) 
} 

trait StringExtensionsStrategy extends (String => StringExtensions) { 
    final def apply(str: String) = new StringExtensions(str, this) 
    def doSth(str: String): String 
} 

class Strategy1 extends StringExtensionsStrategy { 
    override def doSth(str: String) = "a" 
} 

class Strategy2 extends StringExtensionsStrategy { 
    override def doSth(str: String) = "b" 
} 

def someMethod(implicit strategy: StringExtensionsStrategy) = { 
    val name = "Pawel" 
    name.doSth() 
} 

val ret: String = someMethod(new Strategy1()) 

---

作为评价所提到的，可替换的编码将是这样：

class StringExtensions(str: String, strategy: StringExtensionsStrategy) { 
    def doSth() = strategy.doSth(str) 
} 

trait StringExtensionsStrategy { 
    implicit final def apply(str: String) = new StringExtensions(str, this) 
    def doSth(str: String): String 
} 

class Strategy1 extends StringExtensionsStrategy { 
    override def doSth(str: String) = "a" 
} 

class Strategy2 extends StringExtensionsStrategy { 
    override def doSth(str: String) = "b" 
} 

def someMethod(strategy: StringExtensionsStrategy) = { 
    import strategy._ 
    val name = "Pawel" 
    name.doSth() 
} 

val ret: String = someMethod(new Strategy1())