scala 隐式构造函数参数
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Implicit constructor parameters
提问by Nozdrum
So I tried to work with implicit parameters and variables for the first time and this is working perfectly fine
所以我第一次尝试使用隐式参数和变量，这工作得很好
class Test(implicit val a: Int) {
bar(5)
def bar(c: Int)(implicit d: Int): Unit = {
println(d)
}
}
Then I tried it in some more complex code
然后我在一些更复杂的代码中尝试了它
class GameScreen(val game : Game)(implicit val batch: SpriteBatch, implicit val world: World, implicit val manager: AssetManager) extends Screen {
val camera : OrthographicCamera = new OrthographicCamera
createOpenGLStuff()
createMap()
def createMap(implicit w : World) : Unit =
{
}
But now I get the error
但现在我得到了错误
- not enough arguments for method createMap: (implicit w:
com.badlogic.gdx.physics.box2d.World)Unit. Unspecified value parameter w.
I don't know why this is not working, i can write
我不知道为什么这不起作用，我可以写
createMap(this.world)
And all is well, but since this.world is implicit ( I think? ) I should not need to specify it there. What am I doing/understanding wrong here?
一切都很好，但是由于 this.world 是隐式的（我认为？）我不需要在那里指定它。我在这里做什么/理解错了？
回答by Marius Danila
You need to drop the parens
你需要去掉括号
class GameScreen(val game : Game)(implicit val batch: SpriteBatch, implicit val world: World, implicit val manager: AssetManager) extends Screen {
val camera : OrthographicCamera = new OrthographicCamera
createOpenGLStuff()
createMap //this works
def createMap(implicit w : World) : Unit =
{
}
However, the createMap method has to perform some side-effects, so calling it without parens isn't really a good thing.
但是，createMap 方法必须执行一些副作用，因此在没有括号的情况下调用它并不是一件好事。
I suggest changing to:
我建议改为：
def createMap()(implicit w : World) : Unit = {
...
}
This way, you get to maintain the original calling syntax: createMap()
这样，您就可以保持原来的调用语法： createMap()
回答by Brandon Mott
Also, you only need the implicit keyword at the beginning of the parameter list:
此外，您只需要参数列表开头的隐式关键字：
class GameScreen(val game : Game)(implicit val batch: SpriteBatch, val world: World, val manager: AssetManager) extends Screen {...}
