docs/csharp/language-reference/keywords/snippets/ParameterModifiers.cs - main - aprogrammer/dotnet-docs

docs/csharp/language-reference/keywords/snippets/ParameterModifiers.cs
150 строк5 KB
Bill Wagner
Add params collections (#40978)
21 май 2024, 00:01
21 май 2024, 00:0157cbe8e
namespace Keywords;

internal class ParameterModifiers
{
    internal static void ParamPassingExamples()
    {
        // <ParameterPassingExamples>

        // Passing a variable by value means passing a copy of the variable.
        // n1 is a value type
        int n1 = 5;
        System.Console.WriteLine("The value before calling the method: {0}", n1);

        SquareItValue(n1);  // Passing the variable by value.
        System.Console.WriteLine("The value after calling the method: {0}", n1);

        static void SquareItValue(int x)
        // The parameter x is passed by value.
        // Changes to x will not affect the original value of x.
        {
            x *= x;
            System.Console.WriteLine("The value inside the method: {0}", x);
        }
        /* Output:
            The value before calling the method: 5
            The value inside the method: 25
            The value after calling the method: 5
        */

        // arr1 is a reference type
        int[] arr1 = { 1, 4, 5 };
        System.Console.WriteLine("Before calling the method, the first element is: {0}", arr1[0]);

        ChangeValue(arr1);
        System.Console.WriteLine("After calling the method, the first element is: {0}", arr1[0]);

        static void ChangeValue(int[] pArray)
        {
            pArray[0] = 888;  // This change affects the original element.
            pArray = new int[5] { -3, -1, -2, -3, -4 };   // This change is local.
            System.Console.WriteLine("Inside the method, the first element is: {0}", pArray[0]);
        }
        /* Output:
            Before calling the method, the first element is: 1
            Inside the method, the first element is: -3
            After calling the method, the first element is: 888
        */

        // Passing a value by reference means passing a reference to the variable.
        // n is a value type
        int n2 = 5;
        System.Console.WriteLine("The value before calling the method: {0}", n2);

        SquareItReference(ref n2);  // Passing the variable by reference.
        System.Console.WriteLine("The value after calling the method: {0}", n2);

        static void SquareItReference(ref int x)
        // The parameter x is passed by reference.
        // Changes to x will affect the original value of x.
        {
            x *= x;
            System.Console.WriteLine("The value inside the method: {0}", x);
        }
        /* Output:
            The value before calling the method: 5
            The value inside the method: 25
            The value after calling the method: 25
        */

        // arr2 is a reference type
        int[] arr2 = { 1, 4, 5 };
        System.Console.WriteLine("Before calling the method, the first element is: {0}", arr2[0]);

        ChangeItReference(ref arr2);
        System.Console.WriteLine("After calling the method, the first element is: {0}", arr2[0]);

        static void ChangeItReference(ref int[] pArray)
        {
            // Both of the following changes will affect the original variables:
            pArray[0] = 888;
            pArray = new int[5] { -3, -1, -2, -3, -4 };
            System.Console.WriteLine("Inside the method, the first element is: {0}", pArray[0]);
        }
        /* Output:
            Before calling the method, the first element is: 1
            Inside the method, the first element is: -3
            After calling the method, the first element is: -3        */
        // </ParameterPassingExamples>

        TryParamsCalls();
    }

    //<ParamsModifierExamples>
    public static void ParamsModifierExample(params int[] list)
    {
        for (int i = 0; i < list.Length; i++)
        {
            System.Console.Write(list[i] + " ");
        }
        System.Console.WriteLine();
    }

    public static void ParamsModifierObjectExample(params object[] list)
    {
        for (int i = 0; i < list.Length; i++)
        {
            System.Console.Write(list[i] + " ");
        }
        System.Console.WriteLine();
    }

    public static void TryParamsCalls()
    {
        // You can send a comma-separated list of arguments of the
        // specified type.
        ParamsModifierExample(1, 2, 3, 4);
        ParamsModifierObjectExample(1, 'a', "test");

        // A params parameter accepts zero or more arguments.
        // The following calling statement displays only a blank line.
        ParamsModifierObjectExample();

        // An array argument can be passed, as long as the array
        // type matches the parameter type of the method being called.
        int[] myIntArray = { 5, 6, 7, 8, 9 };
        ParamsModifierExample(myIntArray);

        object[] myObjArray = { 2, 'b', "test", "again" };
        ParamsModifierObjectExample(myObjArray);

        // The following call causes a compiler error because the object
        // array cannot be converted into an integer array.
        //ParamsModifierExample(myObjArray);

        // The following call does not cause an error, but the entire
        // integer array becomes the first element of the params array.
        ParamsModifierObjectExample(myIntArray);
    }
    /*
    Output:
        1 2 3 4
        1 a test

        5 6 7 8 9
        2 b test again
        System.Int32[]
    */
    //</ParamsModifierExamples>

}