ref vs out 参数

码

class Program
{
    static void Main(string[] args)
    {
        int a = 20;
        Console.WriteLine("Inside Main - Before Callee: a = {0}", a);
        Callee(a);
        Console.WriteLine("Inside Main - After Callee: a = {0}", a);
        Console.WriteLine();

        Console.WriteLine("Inside Main - Before CalleeRef: a = {0}", a);
        CalleeRef(ref a);
        Console.WriteLine("Inside Main - After CalleeRef: a = {0}", a);
        Console.WriteLine();

        Console.WriteLine("Inside Main - Before CalleeOut: a = {0}", a);
        CalleeOut(out a);
        Console.WriteLine("Inside Main - After CalleeOut: a = {0}", a);
        Console.ReadLine();
    }

    static void Callee(int a)
    {
        a += 5;
        Console.WriteLine("Inside Callee a : {0}", a);
    }

    static void CalleeRef(ref int a)
    {
        a += 10;
        Console.WriteLine("Inside CalleeRef a : {0}", a);
    }

    static void CalleeOut(out int a)
    {
        // can't use a+=15 since for this method 'a' is not intialized only declared in the method declaration
        a = 25; //has to be initialized
        Console.WriteLine("Inside CalleeOut a : {0}", a);
    }
}

输出

Inside Main - Before Callee: a = 20
Inside Callee a : 25
Inside Main - After Callee: a = 20

Inside Main - Before CalleeRef: a = 20
Inside CalleeRef a : 30
Inside Main - After CalleeRef: a = 30

Inside Main - Before CalleeOut: a = 30
Inside CalleeOut a : 25
Inside Main - After CalleeOut: a = 25