scala的隐式转换学习总结（详细）

implicit def 函数名(参数)：返回值类型={
     //函数体
     //返回值
}

//导入对应的规则类，以免出现警告
scala> import scala.language.implicitConversions
import scala.language.implicitConversions
//定义将Int类型的值转换为Float的函数
scala> implicit def int2float(x:Int): Float = x.toFloat
int2float: (x: Int)Float

scala> val x:Float = 2
x: Float = 2.0
scala>

//函数一
scala> implicit def int2float2(x: Float): Int = x.toInt
int2float2: (x: Float)Int
//函数二
scala> implicit def int2float(x: Float): Int = x.toInt
int2float: (x: Float)Int
//调用，报错
scala> val x:Int = 2.55f
<console>:14: error: type mismatch;
 found   : Float(2.55)
 required: Int
Note that implicit conversions are not applicable because they are ambiguous:
 both method int2float2 of type (x: Float)Int
 and method int2float of type (x: Float)Int
 are possible conversion functions from Float(2.55) to Int
       val x:Int = 2.55f
                   ^

implicit class 类名（参数）{
    //类主体
}

scala> implicit class Dog(val name: String){
     | def bark=println(s"$name is barking")}
defined class Dog

scala> "barkdo".bark
barkdo is barking

scala> implicit class Dog2(val name: String, val age: Int){
     | def bark=println(s"$name is barking")}
<console>:15: error: implicit classes must accept exactly one primary constructor parameter
       implicit class Dog2(val name: String, val age: Int){

implicit object 对象名{
    //类主体
}

object ImplicitTest extends App{
   //定义一个trait Multiplicable
  trait Multiplicable[T]{
     def multiply(x: T):T
   }
  //定义一个隐式对象，用于整型数据相乘
  implicit object MultiplicableInt extends Multiplicable[Int]{
    def multiply(x: Int): Int = x*x
  }
  //定义一个用于字符串相乘的隐式对象
  implicit object MultiplicableString extends Multiplicable[String]{
    def multiply(x: String): String = x*2
  }
  //定义一个函数，函数具有泛型参数
  def multiply[T: Multiplicable](x: T): T ={
    //implicitly方法，访问隐式对象
    val ev = implicitly[Multiplicable[T]]
    //根据具体的类型调用相应的隐式对象中的方法
    ev.multiply(x)
  }

  //调用隐式对象 MultiplicableInt 中的方法
  println(multiply(5))

  //调用隐式对象 MultiplicableString 中的方法
  println(multiply("5"))
}

 运行结果：

25
55

def 函数名（implicit 参数名：l类型）:返回值={
       //函数体
}

 //定义一个函数，函数具有泛型参数
  def multiply[T: Multiplicable](x: T)(implicit ev: Multiplicable[T]): T ={
    //根据具体的类型调用相应的隐式对象中的方法
    ev.multiply(x)
  }

implicit val 变量名：类型=值

//定义一个带隐式参数的函数
scala> def sqrt(implicit x: Double) = Math.sqrt(x)
sqrt: (implicit x: Double)Double
//定义一个隐式值
scala> implicit val x:Double = 2.55
x: Double = 2.55
//调用定义的sqrt函数，它将自行调用定义好的隐式值
scala> sqrt
res1: Double = 1.5968719422671311

scala> def product(implicit x: Double, implicit y: Double)=x*y
<console>:1: error: identifier expected but 'implicit' found.
def product(implicit x: Double, implicit y: Double)=x*y

scala> def product(implicit x: Double)(implicit y: Double)=x*y  //柯里化函数
<console>:1: error: '=' expected but '(' found.
def product(implicit x: Double)(implicit y: Double)=x*y

scala> val prodeuct = (x: Double, y: Double) => x*y
prodeuct: (Double, Double) => Double = <function2>

scala> val prodeuct = (implicit x: Double, y: Double) => x*y
<console>:1: error: '=>' expected but ',' found.
val prodeuct = (implicit x: Double, y: Double) => x*y
                                  ^

//柯里化函数product
scala> def product(x: Double)(y: Double)=x*y
product: (x: Double)(y: Double)Double
//两个参数的偏应用函数
scala> val p1=product _
p1: Double => (Double => Double) = <function1>
//调用
scala> p1(3.0)(4.0)
res1: Double = 12.0
//一个参数的偏应用函数
scala> val p2 = product(3.0) _
p2: Double => Double = <function1>
//调用
scala> p2(4.0)
res2: Double = 12.0
//将柯里化函数参数y, 声明为隐式参数
scala> def product(x: Double)(implicit y: Double)=x*y
product: (x: Double)(implicit y: Double)Double
//定义隐式参数后，便不能使用其偏应用函数
scala> val p1=product _
<console>:13: error: could not find implicit value for parameter y: Double
       val p1=product _
              ^
scala>