Scala 部分应用不清楚

Question

我不是很清楚Scala中函数的部分应用......
我会做一个例子:

def myOperation(x: Int)(y: Int): Int = {
    val complexVal = complexCalc(x)
    println("complexVal calculated")
    complexVal + y
}
def complexCalc(x: Int): Int = x * 2

val partial = myOperation(5)_

println("calculate")
println("result(3): " + partial(3))
println("result(1): " + partial(1))

输出将是:

calculate
complexVal calculated
result(3): 13
complexVal calculated
result(1): 11

所以 complexVal被计算了 2 次，如果我只想计算一次怎么办？

对于谁拥有 javascript 知识，例如:

function myOperation(x) {
     var complexVal = complexCalc(x)
     return function(y){
         complexVal + y
     }
}

编辑 :
那么我之前写的和这个有什么区别:

def myOperation2(x: Int, y: Int): Int = {
    val complexVal = complexCalculation(x)
    println("complexVal calculated")
    complexVal + y
}

val partial = myOperation(5)_
val partial2 = myOperation2(5, _: Int)

Answer 1

您可以从 myOperation 显式返回一个函数:

def myOperation(x: Int): Int => Int = {
    val complexVal = complexCalc(x)
    println("complexVal calculated")
    (y: Int) => complexVal + y
}