Question

我想用动态算子创建一个动态算术表达式。

我对迅捷很新，以下是完全虚假的，但我想的是：

class Expr {
  var operandA:Double = 0;
  var operandB:Double = 0;
  var arithmeticOperator:operator = +; // total bogus

  init( a operandA:Double, b operandB:Double, o arithmeticOperator:operator ) {
    self.operandA = operandA;
    self.operandB = operandB;
    self.arithmeticOperator = arithmeticOperator;
  }

  func calculate() -> Double {
    return self.operandA self.arithmeticOperator self.operandB; // evaluate the expression, somehow
  }
}

var expr = Expr( a: 2, b: 5, o: * );
expr.calculate(); // 10

类似的东西是否可行，不知何故（没有定义操作函数/方法）？

Answer 1

最接近的是，我可以使用自定义字符作为运算符，然后使用switch case来计算表达式，

protocol Arithmetic{
  func + (a: Self, b: Self) -> Self
  func - (a:Self, b: Self ) -> Self
  func * (a:Self, b: Self ) -> Self
}

extension Int: Arithmetic {}
extension Double: Arithmetic {}
extension Float: Arithmetic {}


class Expr<T:Arithmetic>{
  let operand1: T
  let operand2: T
  let arithmeticOperator: Character

  init( a operandA:T, b operandB:T, o arithmeticOperator:Character) {
    operand1 = operandA
    operand2 = operandB
    self.arithmeticOperator = arithmeticOperator
  }

  func calculate() -> T? {
    switch arithmeticOperator{
      case "+":
      return operand1 + operand2
      case "*":
      return operand1 * operand2
      case "-":
      return operand1 - operand2
     default:
      return nil
    }
  }
}

var expr = Expr( a: 2, b: 5, o: "+" );
expr.calculate();

是否可以使用动态运算符创建动态算术表达式？

1 个答案: