Created
August 22, 2010 19:08
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/* | |
implicit parameterを参照するには、コンパニオンオブジェクト内の定義を探す場合も、その定義位置より後でないとダメみたい。 | |
以下のコードだと | |
error: could not find implicit value for evidence parameter of type RichGraphics.Drawer[MyLine] | |
g.draw(MyLine(10, 30, 50, 20)) | |
というエラーになる。 | |
new Frame { ... } の部分をコードの一番最後に移動すると、 | |
うまく動くようになる。 | |
*/ | |
import swing._ | |
import java.awt.Graphics2D | |
new Frame { | |
contents = new BorderPanel { | |
preferredSize = new Dimension(100, 100) | |
override def paintComponent(g:Graphics2D) { | |
implicit def enrichGraphics(g: Graphics2D) = new RichGraphics(g) | |
g.draw(MyLine(10, 30, 50, 20)) | |
g.draw(MyRect(40, 40, 20, 20)) | |
} | |
} | |
visible = true | |
} | |
case class MyLine(x1: Int, y1: Int, x2: Int, y2: Int) | |
case class MyRect(x: Int, y: Int, w: Int, h: Int) | |
object RichGraphics { | |
trait Drawer[T] { | |
def draw(g: Graphics2D, target: T) | |
} | |
implicit object myLineDrawer extends Drawer[MyLine] { | |
def draw(g: Graphics2D, t: MyLine) = | |
g.drawLine(t.x1, t.y1, t.x2, t.y2) | |
} | |
implicit object myRectDrawer extends Drawer[MyRect] { | |
def draw(g: Graphics2D, t: MyRect) = | |
g.drawRect(t.x, t.y, t.w, t.h) | |
} | |
} | |
class RichGraphics(g: Graphics2D) { | |
def draw[T: RichGraphics.Drawer](target: T) = | |
implicitly[RichGraphics.Drawer[T]].draw(g, target) | |
} |
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