C #4.0 optional parameters

One of the new features in C #4.0 is named parameters and optional parameters.

Naming parameters: when calling a method, you can specify the parameter name instead of passing parameters by location;

Private void func (string STR, int number, bool flag ){}

For the above functions, the name parameter can be fun (FLAG: True, Number: 10, STR: "zhangsan ");

Optional parameters: When declaring a parameter in a method, you can set the default value for it. When calling this method, this optional parameter can be ignored. The following principles must be followed:

1. The optional parameter must have a compile time as its default value. If it is a reference type other than string (including the SpecialDynamic type). The default value can only be null.

Private void func (string STR, int A = 10, people P = new people () is not compiled;

2. The optional parameter must appear after the non-optional parameter. The parameter on the right of the optional parameter (if any) must be an optional parameter.

Private void func (string STR, int A = 10, bool flag) This statement is not compiled;

Use private void func (string name, int age = 10, bool sex = false) {// do something;} as an example to describe how to call the named parameters and optional parameters: 

This. func ("zhangsan"); // ignore all optional parameters
This. func (sex: True, age: 30, name: "zhangsan"); // use the name parameter to change the order;
This. func ("zhangsan", 20); // use the preceding optional parameters in sequence without the optional parameter name;
This. func ("zhangsan", 30, true); // use all optional parameters without the optional parameter name;
This. func ("zhangsan", sex: false); // if you use the following optional parameter, you must use the optional parameter name; this. func ("zhangsan", false); cannot be compiled;
This. func ("zhangsan", age: 40 );

The preceding call methods are correct;