C # syntax sugar ($) (?. ）（?? ）

Interpolated string ($)

is actually a C # 6.0 pair string. Improved format, identifying string literals as interpolated strings ($)
According to Microsoft's example:

1 usingSystem;2 3  Public classExample4 {5     Public Static voidMain ()6    {7       stringName ="John";8       stringGreeting = $"Hello, {name}!";9 Console.WriteLine (greeting);Ten    } One}

Equivalent to the original string. Format must use placeholders, which are extremely error-prone:

1 string " John " ; 2 string string. Fromat ("hello,{0}! ", name);

The use of $ is not prone to errors and can be written like this:

1 string " John " ; 2 string str = $"hello,{name}! ";

Added syntax sugar: (?. ）

This is also the syntax of c#6.0, which is called null-conditional Operator (null conditional operator)
We often need to determine whether the object is null (not judging it will report the exception system.nullreferenceexception), we generally like this:

1 list<stringnull; 2 if NULL )3{4     string[] Strarr = list. ToArray (); 5 }

or this:

1 list<stringnull; 2 string NULL null);

This can be done simply by using this null-conditional operator.

1 list<stringnull; 2 string [] Strarr = list?. ToArray ();

Explain that when the list is null, it does not take the following toarray (), returns NULL when the list is not null toarray ();
Notice here that the front Strarr this is a nullable value.

The null merge operator (?? ）

?? operator is called a null merge operator. If the left operand of this operator is not NULL, this operator returns the left operand, otherwise the right operand is returned.
Demo:

1 int null; // a nullable int is set in front of it, so it becomes 0 when you want null. 2 int 0;

C # syntax sugar ($) (?. ）（?? ）