在c＃3.0中，是否可以在字符串类中添加隐式运算符？

Question

something like

public static class StringHelpers
{
    public static char first(this string p1)
    {
        return p1[0];
    }

    public static implicit operator Int32(this string s) //this doesn't work
    {
        return Int32.Parse(s);
    }
}

so :

string str = "123";
char oneLetter = str.first(); //oneLetter = '1'

int answer = str; // Cannot implicitly convert ...

Answer 1

No, there's no such thing as extension operators (or properties etc) - only extension methods .

The C# team have considered it - there are various interesting things one could do (imagine extension constructors) - but it's not in C# 3.0 or 4.0. See Eric Lippert's blog for more information (as always).

Answer 2

  /// <summary>
    /// 
    /// Implicit conversion is overloadable operator
    /// In below example i define fakedDouble which can be implicitly cast to touble thanks to implicit operator implemented below
    /// </summary>

    class FakeDoble
    {

        public string FakedNumber { get; set; }

        public FakeDoble(string number)
        {
            FakedNumber = number;
        }

        public static implicit operator double(FakeDoble f)
        {
            return Int32.Parse(f.FakedNumber);
        }
    }

    class Program
    {

        static void Main()
        {
            FakeDoble test = new FakeDoble("123");
            double x = test; //posible thanks to implicit operator

        }

    }

Answer 3

Unfortunately C# does not allow you to add operators to any types that you don't own. Your extension method is about as close as you are going to get.

Answer 4

What you are trying to do in your example (defining an implicit operation from string to int) is not allowed.

Since an operation (implicit OR explicit) can only be defined in the class definition of the target or destination class, you cannot define your own operations between framework types.

Answer 5

I am thinking your best bet is something like this:

public static Int32 ToInt32(this string value)
{
    return Int32.Parse(value);
}