使用委托实现

加减乘除拥有相同的参数个数、类型和返回类型，首先想到了使用委托实现。



//创建一个委托
public delegate decimal MathOperation(decimal left, decimal right);

//创建方法参数和返回结果符合委托的定义
public static decimal Add(decimal left, decimal right)
{
    return left + right;
}

public static decimal Subtract(decimal left, decimal right)
{
    return left - right;
}

public static decimal Multiply(decimal left, decimal right)
{
    return left * right;
}

public static decimal Divide(decimal left, decimal right)
{
    return left / right;
}

//返回委托类型
private static MathOperation GetOperation(char oper)
{
    switch(oper)
    {
        case '+': return Add;
        case '-': return Subtract;
        case '*': return Multiply;
        case '/': return Divide;
    }

    throw new NotSupportedException("");
}

//封装一个方法用来把操作数和符号考虑进来,返回委托类型
private static decimal Eval(string expr)
{
    var elements = expr.Split(new []{' '}, 3);
    var left = Decimal.Parse(elements[0]);
    var right = Decimal.Parse(elements[1]);
    var ope = elements[2][0];

    return GetOperation(op)(left, right);
}

void Main()
{
    Console.WriteLine(Eval("1 3 +"));
}


 

使用接口实现

以上，委托用在了方法层面。如果在类层面，也可用接口封装加减乘除的共性。



public interface IMathOperation
{
    decimal Compute(decimal left, decimal right);
}

public class AddOperation : IMathOperation
{
    decimal Compute(decimal left, decimal right)
    {
        return left + right;
    }
}

public class SubtractOperation : IMathOperation
{
    decimal Compute(decimal left,, decimal right)
    {
        return left - right;
    }
}

public class MultiplyOperation : IMathOperation
{
    decimal Compute(decimal left, decimal right)
    {
        return left * right;
    }
}

public class DivideOperation : IMathOperation
{
    decimal Compute(decimal left, decimal right)
    {
        return left/right;
    }
}

//获取接口类型
private static IMathOperation GetOperation(char oper)
{
    switch(oper)
    {
        case '+': return new AddOperation();
        case '-': return new SubtractOperation();
        case '*': return new MultiplyOperation();
        case '/': return new DivideOperation();
    }

    throw new NotSupportedException("");
}

...


使用匿名方法

委托还可以结合匿名方法一起使用



public delegate decimal MathOperation(decimal left, decimal right);

private static MathOperation GetOperation(char oper)
{
    switch(oper)
    {
        case '+': return delgate(decimal left, decimal right) {return left + right;};
        case '-': return delgate(decimal left, decimal right) {return left - right;};
        case '*': return delgate(decimal left, decimal right) {return left * right;};
        case '/': return delgate(decimal left, decimal right) {return left / right;};
    }

    throw new NotSupportedException("");
}


泛型委托

而用泛型委托实现更简洁。



private static Func<decimal, decimal, decimal> GetOperation(char oper)
{
    switch(oper)
    {
        case '+': return (left, right) => left + right;
        case '-': return (left, right) => left - right;
        case '*': return (left, right) => left * right;
        case '/': return (left, right) => left / right;
    }

    throw new NotSupportedExcepton("");
}