C#中使用委托、介面、匿名方法、泛型委托實現加減乘除演算法

使用C#實現加減乘除演算法經常被用作新手練習。本篇來分別體驗通過委托、介面、匿名方法、泛型委托來實現。

使用委托實現

加減乘除擁有相同的參數個數、類型和返回類型，首先想到了使用委托實現。

//創建一個委托
public delegate decimal MathOperation(decimal left, decimal right);

//創建方法參數和返回結果符合委托的定義
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;
}

//返回委托類型
private static MathOperation GetOperation(char oper)
{
    switch(oper)
    {
        case '+': return Add;
        case '-': return Subtract;
        case '*': return Multiply;
        case '/': return Divide;
    }
    
    throw new NotSupportedException("");
}

//封裝一個方法用來把操作數和符號考慮進來,返回委托類型
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 +"));
}

使用介面實現

以上，委托用在了方法層面。如果在類層面，也可用介面封裝加減乘除的共性。

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;
    }
}

//獲取介面類型
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

委托還可以結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

而用泛型委托實現更簡潔。

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("");
}

暫時這些。