奇怪斯卡拉錯誤

我試圖創建抽象的回合制遊戲和人工智能（AI）：奇怪斯卡拉錯誤

abstract class AGame { 
    type Player 
    type Move  // Player inside 

    def actPlayer : Player 
    def moves (player : Player) : Iterator[Move] 
    def play (move : Move) 
    def undo() 
    def isFinished : Boolean 
    def result (player : Player) : Double 
} 

abstract class Ai[Game <: AGame] { 
    def genMove (player : Game#Player) : Game#Move 
} 

class DummyGame extends AGame { 
    type Player = Unit 
    type Move = Unit 

    def moves (player : Player) = new Iterator[Move] { 
    def hasNext = false 
    def next = throw new Exception ("asd") 
    } 

    def actPlayer =() 

    def play (move : Move) { 
    } 

    def undo() { 
    } 

    def isFinished = true 

    def result (player : Player) = 0 
} 

class DummyAi[Game <: AGame] (game : Game) extends Ai[Game] { 
    override def genMove (player : Game#Player) : Game#Move = { 
    game.moves (player).next 
    } 
}

我認爲我必須使用這種奇怪的類型存取像遊戲＃球員。我得到非常令人費解的錯誤。我想了解：

[error] /home/lew/Devel/CGSearch/src/main/scala/Main.scala:41: type mismatch; 
[error] found : Game#Player 
[error] required: DummyAi.this.game.Player 
[error]  game.moves (player).next 
[error]    ^

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2010-06-13 Łukasz Lew

這應該是'game.moves（player）.next'還是'game.moves（player.next）'？ Scala語法對於兩種解釋都是不明確的，但解析器需要選擇一種語法。 – Theo 2010-06-13 17:41:35

從錯誤消息中可以清楚地看到它被解析爲第一個。 – 2010-06-13 18:59:32

def moves (player : Player)意味着moves接受這Game的球員。

Game#Player是玩家的類型任何Game。所以moves (player)是一種類型不匹配。

下面是一個簡單的例子，它顯示了爲什麼它必須是不匹配。假如它不是，看看接下來會發生什麼：

class Game2 extends DummyGame { 
    override type Player = Boolean 
    override type Move = Boolean 

    override def moves(player : Boolean) = new Iterator[Boolean] {...} 
} 

val game2: DummyGame = new Game2 
// game2.Player is Boolean 

val dummyGameAi = new DummyAi[DummyGame](game2) 
// DummyGame#Player == Unit, so the type of genMove for Ai[DummyGame] is 
// def genMove (player : Unit) : Unit 

dummyGameAi.genMove(()) 
// this calls game2.moves(()), which doesn't typecheck

爲了得到這個工作，我們可以改變的genMove類型。如果我們通過遊戲作爲參數（這是有道理的呢），我們可以用路徑依賴類型：

abstract class Ai[Game <: AGame] { 
    def genMove (game : Game)(player : game.Player) : game.Move 
    // now game.moves (player) typechecks 
}

來源

2010-06-13 18:26:13

我明白，但我仍然不知道該如何解決這個問題。任何想法 – 2010-06-13 22:27:28

不會導致非法依賴方法類型錯誤？ – BenjaminJackman 2010-06-14 19:16:46

你使用了'-Xexperimental'選項嗎？ http://lampsvn.epfl.ch/trac/scala/ticket/128 – 2010-06-14 19:51:16

您可以通過在Ai引入抽象成員game解決你的問題，然後指定的路徑依賴使用此成員類型：

abstract class Ai[Game <: AGame] { 
    val game : Game 
    def genMove (player : game.Player) : game.Move 
} 

class DummyAi[Game <: AGame] (val game : Game) extends Ai[Game] { 
    override def genMove (player : game.Player) : game.Move = { 
    game.moves (player).next 
    } 
}

來源

2010-06-14 09:08:04

奇怪斯卡拉錯誤

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