Scala_方法、函數、柯里化

方法、函數、柯里化

方法

• 聲明方法：

scala> def m1(x:Int,y:Int):Int = {
     | x + y
     | }
m1: (x: Int, y: Int)Int
scala> m1(3,5)
res6: Int = 8

函數

• 函數聲明

scala> val f1 = (x: Int, y: Int) => x + y
f1: (Int, Int) => Int = <function2> //2是指參數的個數
scala> f1(3,5)
res7: Int = 8
//函數做爲參數傳入方法
scala> def m2(f: (Int , Int) => Int , x: Int) = f(3,4)
m2: (f: (Int, Int) => Int, x: Int)Int
scala> def m2(f: (Int , Int) => Int , x: Int) = f(3,4) + x
m2: (f: (Int, Int) => Int, x: Int)Int
scala> val f1 = (x: Int, y: Int) => x + y
f1: (Int, Int) => Int = <function2>
scala> m2(f1,2)
res8: Int = 9
//方法轉換爲函數
​

方法轉換爲函數

scala> def m2(f: (Int , Int) => Int , x: Int) = f(3,4)
m2: (f: (Int, Int) => Int, x: Int)Int
​
scala>  def m1(x:Int,y:Int):Int = x + y
m1: (x: Int, y: Int)Int
​
scala> val f1 = m1 _  //方法m1轉換爲函數
f1: (Int, Int) => Int = <function2>
scala> m2(f1,2)
res9: Int = 9
scala> m2(m1,2) //m1隱式轉換爲函數了
res10: Int = 9

柯里化

• 柯里化（Currying）是把接受多個參數的函數變換成接受一個單一參數(最初函數的第一個參數)的函數，而且返回接受餘下的參數且返回結果的新函數的技術

• 聲明方法

// 聲明方式1
scala> def currying(x: Int)(y:Int) = x*y
currying: (x: Int)(y: Int)Int
​
scala> currying(3)(4)
res0: Int = 12
​
scala> val curry = currying(3)_
curry: Int => Int = <function1>
​
scala> curry(2)
res1: Int = 6
​
scala> curry(9)
res2: Int = 27
​
// 聲明方式2
scala> def curry(x: Int) = (y: Int) => x * y
curry: (x: Int)Int => Int
​
scala> val fun = curry(2)
fun: Int => Int = <function1>
​
scala> fun(2)
res10: Int = 4

• 柯里化設置隱式的值

scala> def m2(x: Int)(implicit y: Int = 5) = x * y
m2: (x: Int)(implicit y: Int)Int
​
scala> m2(5)
res3: Int = 25
​
scala> m2(4)(4)
res4: Int = 16
​
scala> implicit val a = 100
a: Int = 100
​
scala> m2(4)
res5: Int = 400
​
scala> m2(4)(10)
res6: Int = 40
​
scala> implicit val b = 200
b: Int = 200
​
scala> m2(4)
<console>:11: error: ambiguous implicit values:
 both value a of type => Int
 and value b of type => Int
 match expected type Int
              m2(4)
                ^