#1,207 – C# 6.0 – Auto-Property Initializers for Read-Only Properties

Prior to C# 6.0, if you wanted a read-only (immutable) property, you’d typically use a read-only backing field that is initialized in the constructor, as shown below.

    public class Dog 
    {
        public string Name { get; set; }

        // DogCreationTime is immutable
        private readonly DateTime creTime;
        public DateTime DogCreationTime 
        {
            get { return creTime; }
        }

        public Dog(string name)
        {
            Name = name;
            creTime = DateTime.Now;
        }
    }

In C# 6.0, you can use auto-implemented properties to implement a read-only property.  You do this by using an auto-property initializer.  The result is much cleaner than the above example, where we had to explicitly declare a backing field.

    public class Dog
    {
        public string Name { get; set; }

        // DogCreationTime is immutable
        public DateTime DogCreationTime { get; } = DateTime.Now;

        public Dog(string name)
        {
            Name = name;
        }
    }

#1,206 – C# 6.0 – Auto-Property Initializers

C# 3.0 introduced auto-implemented properties.

Older syntax:

private string name = "default";
public string Name
{
    get { return name; }
    set { name = value; }
}

Improved syntax, using auto-implemented properties:

public string Name { get; set; }

The new syntax provided no mechanism for specifying a default property value. To specify a default value, you either needed to go back to using an explicit backing variable or to set the default value from within a constructor.

C# 6.0 supports specifying default values for auto-implemented properties, as shown below.

        public string Name { get; set; } = "default";

#1,205 – C# 6.0 – Using the Null-Conditional when Invoking a Delegate

When you fire an event (by invoking a delegate), you typically need to check for null before invocation.  This avoids a null reference exception if there are no subscribers to the event.

    public class Dog
    {
        public Dog(string name, int age)
        {
            Name = name;
            Age = age;
        }

        public event EventHandler<string> NameChange;

        private string name;
        public string Name
        {
            get { return name; }
            set
            {
                if (value != name)
                {
                    name = value;

                    // Check for null before invocation
                    if (NameChange != null)
                    {
                        NameChange(this, name);
                    }
                }
            }
        }

        public int Age { get; set; }
    }

(The above pattern is not thread-safe).

An alternative pattern is to declare the event with a null handler, so that there is always at least one handler on the invocation list. (This is thread-safe).

In C# 6.0, we can use the null-conditional to invoke a delegate.

                    NameChange?.Invoke(this, name);

#1,204 – C# 6.0 – Using Null-Conditional with Indexer

The new null-conditional operator in C# 6.0 allows checking for null and de-referencing a variable in a single step.

You can use the null-conditional operator with dot (.) notation, to access an object’s properties or to invoke a method.  You can also use the null-conditional with an indexer, as shown below.  The expression returns the value returned by the indexer if the variable is non-null, or returns null if the variable is null.

            string sTest = "Howdy";

            char? thirdChar = sTest?[2];   // 'w'

            sTest = null;
            thirdChar = sTest?[2];   // null

            sTest = "Ho";
            thirdChar = sTest?[2];   // throws IndexOutOfRangeException

Notice that the null-conditional operator protects you from de-referencing a null pointer, but does not protect you from using an index that is longer than the string length.