深入解析C#中的命名实参和可选实参

CalculateBMI(weight: 123, height: 64);CalculateBMI(height: 64, weight: 123);

CalculateBMI(123, height: 64);

CalculateBMI(weight: 123, 64);

class NamedExample{  static void Main(string[] args)  {    // The method can be called in the normal way, by using positional arguments.    Console.WriteLine(CalculateBMI(123, 64));    // Named arguments can be supplied for the parameters in either order.    Console.WriteLine(CalculateBMI(weight: 123, height: 64));    Console.WriteLine(CalculateBMI(height: 64, weight: 123));    // Positional arguments cannot follow named arguments.    // The following statement causes a compiler error.    //Console.WriteLine(CalculateBMI(weight: 123, 64));    // Named arguments can follow positional arguments.    Console.WriteLine(CalculateBMI(123, height: 64));  }  static int CalculateBMI(int weight, int height)  {    return (weight * 703) / (height * height);  }}

public void ExampleMethod(int required, string optionalstr = "default string",  int optionalint = 10)

anExample.ExampleMethod(3, ,4);

anExample.ExampleMethod(3, optionalint: 4);

namespace OptionalNamespace{  class OptionalExample  {    static void Main(string[] args)    {      // Instance anExample does not send an argument for the constructor's      // optional parameter.      ExampleClass anExample = new ExampleClass();      anExample.ExampleMethod(1, "One", 1);      anExample.ExampleMethod(2, "Two");      anExample.ExampleMethod(3);      // Instance anotherExample sends an argument for the constructor's      // optional parameter.      ExampleClass anotherExample = new ExampleClass("Provided name");      anotherExample.ExampleMethod(1, "One", 1);      anotherExample.ExampleMethod(2, "Two");      anotherExample.ExampleMethod(3);      // The following statements produce compiler errors.      // An argument must be supplied for the first parameter, and it      // must be an integer.      //anExample.ExampleMethod("One", 1);      //anExample.ExampleMethod();      // You cannot leave a gap in the provided arguments.       //anExample.ExampleMethod(3, ,4);      //anExample.ExampleMethod(3, 4);      // You can use a named parameter to make the previous       // statement work.      anExample.ExampleMethod(3, optionalint: 4);    }  }  class ExampleClass  {    private string _name;    // Because the parameter for the constructor, name, has a default    // value assigned to it, it is optional.    public ExampleClass(string name = "Default name")    {      _name = name;    }    // The first parameter, required, has no default value assigned    // to it. Therefore, it is not optional. Both optionalstr and     // optionalint have default values assigned to them. They are optional.    public void ExampleMethod(int required, string optionalstr = "default string",      int optionalint = 10)    {      Console.WriteLine("{0}: {1}, {2}, and {3}.", _name, required, optionalstr,        optionalint);    }  }}

Default name: 1, One, and 1.Default name: 2, Two, and 10.Default name: 3, default string, and 10.Provided name: 1, One, and 1.Provided name: 2, Two, and 10.Provided name: 3, default string, and 10.Default name: 3, default string, and 4.

// In C# 3.0 and earlier versions, you need to supply an argument for// every parameter. The following call specifies a value for the first// parameter, and sends a placeholder value for the other six. The// default values are used for those parameters.var excelApp = new Microsoft.Office.Interop.Excel.Application();excelApp.Workbooks.Add();excelApp.Visible = true;var myFormat =   Microsoft.Office.Interop.Excel.XlRangeAutoFormat.xlRangeAutoFormatAccounting1;excelApp.get_Range("A1", "B4").AutoFormat(myFormat, Type.Missing,   Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);

// The following code shows the same call to AutoFormat in C# 4.0. Only// the argument for which you want to provide a specific value is listed.excelApp.Range["A1", "B4"].AutoFormat( Format: myFormat );