如何将一个lambda表达式对象分配给另一个？

Question

var opSpecBoolVal = false
val equalCheck = (x: Int, y: Int) => x == y
val greaterthanCheck = (x: Int, y: Int) => x > y
val lessthanCheck = (x: Int, y: Int) => x < y
val notEqualCheck = (x: Int, y: Int) => x != y

operatorType match {
   case "_equal" => opSpecBoolVal = false; exitCheck = equalCheck; 
   case "_greaterthan" => opSpecBoolVal = true; exitCheck = greaterthanCheck; 
   case "_lessthan" => opSpecBoolVal = false; exitCheck = lessthanCheck; 
   case "_notequal" => opSpecBoolVal = true; exitCheck = notEqualCheck;
}
exitCheck(10, 20)

val exitCheck = operatorType match {
   case "_equal" => equalCheck; 
   case "_greaterthan" => greaterthanCheck; 
   case "_lessthan" => lessthanCheck; 
   case "_notequal" => notEqualCheck;
}

Answer 1

试试看

val exitCheck: (Int, Int) => Boolean = operatorType match {
  case "_equal" =>
    opSpecBoolVal = false
    _ == _

  case "_greaterthan" =>
    opSpecBoolVal = true
    _ > _

  case "_lessthan" =>
    opSpecBoolVal = false
    _ < _

  case "_notequal" =>
    opSpecBoolVal = true
    _ != _
}

哪些产出

val operatorType = "_greaterthan"
exitCheck(10, 20) // res0: Boolean = false

为了避免将var opspecboolval设置为副作用，请尝试一个替代的纯实现，如下所示

type OperatorType = String
type Operator = (Int, Int) => Boolean
type IsSpecialOp = Boolean

val toOp: OperatorType => (Operator, IsSpecialOp) =
{
  case "_equal" => (_ == _, false)
  case "_greaterthan" => (_ > _, true)
  case "_lessthan" => (_ < _, false)
  case "_notequal" => (_ != _, true)
}

val (exitCheck, opSpecBoolVal) = toOp("_greaterthan")
exitCheck(10, 20) // res0: Boolean = false
opSpecBoolVal // res1: IsSpecialOp = true