有沒有辦法要求具有特定參數的構造函數？

Question

我認爲我想要做的事很容易，但我沒有得到正確的搜索關鍵詞。我想要的是保證所有實現類都具有可以用已知類型的對象調用的構造函數的特徵。語法應該是：

trait Message { 
    def this(rdr: msgpack.MsgReader): Message 
} 

但編譯器告訴我它期望等號。任何想法如何做到這一點？

Answer 1

使用類型類模式，而不是：

trait Message[T] { 
    def read(reader: msgpack.MsgReader): T 
    // Example of what would be a normal instance method. 
    // thiz is similar to this, except because we're in another object it must be explicitly taken as parameter. 
    // It's in a separate param list for convention and ease of currying 
    def foo(thiz: T)(param1: Int): Boolean 
} 

// "Implementors" don't actually implement it, the behavior exists as its own singleton 
class Foo { ... } 

implicit object FooMessage extends Message[Foo] { 
    // Note that this is not restricted to just constructors. If you want that then you are really out of luck. (And probably doing it wrong.) 
    override def read(reader: msgpack.MsgReader) = ??? 
    override def foo(thiz: Foo)(param1: Int) = thiz.foo(param1) 
} 

// Usage 
// Use an explicit, named implicit param to avoid implicitly 
def readMsg[T: Message](reader: msgpack.MsgReader) = implicitly[Message[T]].read(reader) 

val foo = readMsg[Foo](???)