C syntax sugar empty merge operator [?] And null merge assignment operator [? =]

Example

for instance : We have a UserInformation class

public class UserInformation
    { 
        public string Name { get; set; }
        public List<string> Address { get; set; }
    }

There's the following code , Let's get Zhang San's first address , If the address is empty , Then return to Shanghai , The usual practice is as follows

static void Main(string[] args)
        {
            UserInformation user = new UserInformation();
            user.Name = " Zhang San ";
            user.Address = null;
            string address = user.Address?.First();
            if (address == null)
            {
                address = " Shanghai ";
            }
        }

So Microsoft engineers think that since we can use ？. This type of optimization attribute is null , Then can we judge when the calculation result is empty , Assign him a value ？ So Microsoft engineers say do it , So the empty merge operator came into being , Our code becomes

static void Main(string[] args)
        {
            UserInformation user = new UserInformation();
            user.Name = " Zhang San ";
            user.Address = null;
            string address = user.Address?.First()??" Shanghai ";
        }

Of course, some friends said , This does not seem to satisfy a situation , For example, when our Address It's empty time , How to give User.address Assignment ？, It can only be written in this mode , Treat the symptoms, not the root cause .

UserInformation user = new UserInformation();
            user.Name = " Zhang San ";
            user.Address = null;
            if (user.Address == null)
            {
                user.Address= new List<string> { " Shanghai " };
            }

So Microsoft engineers think you underestimate me , Say I treat the symptoms but not the root cause , I won't accept it , I have to make an empty merge assignment operator , So this code becomes

static void Main(string[] args)
        {
            UserInformation user = new UserInformation();
            user.Name = " Zhang San ";
            user.Address = null;
            user.Address??= new List<string> { " Shanghai " };
        }

That's the end of today's presentation ,

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