Should C# have a lazy key word

Question

Should C# have a lazy keyword to make lazy initialization easier?

E.g.

    public lazy string LazyInitializeString = GetStringFromDatabase();

instead of

    private string _backingField;

    public string LazyInitializeString
    {
        get
        {
            if (_backingField == null)
                _backingField = GetStringFromDatabase();
            return _backingField;
        }
    }

Answer 1

I don't know about a keyword but it now has a System.Lazy<T> type.

• It is officially part of .Net Framework 4.0.
• It allows lazy loading of a value for a member.
• It supports a lambda expression or a method to provide a value.

Example:

public class ClassWithLazyMember
{
    Lazy<String> lazySource;
    public String LazyValue
    {
        get
        {
            if (lazySource == null)
            {
                lazySource = new Lazy<String>(GetStringFromDatabase);
                // Same as lazySource = new Lazy<String>(() => "Hello, Lazy World!");
                // or lazySource = new Lazy<String>(() => GetStringFromDatabase());
            }
            return lazySource.Value;
        }
    }

    public String GetStringFromDatabase()
    {
        return "Hello, Lazy World!";
    }
}

Test:

var obj = new ClassWithLazyMember();

MessageBox.Show(obj.LazyValue); // Calls GetStringFromDatabase()
MessageBox.Show(obj.LazyValue); // Does not call GetStringFromDatabase()

In above Test code, GetStringFromDatabase() gets called only once. I think that is exactly what you want.

Edit:

After having comments from @dthorpe and @Joe, all I can say is following is the shortest it can be:

public class ClassWithLazyMember
{
    Lazy<String> lazySource;
    public String LazyValue { get { return lazySource.Value; } }

    public ClassWithLazyMember()
    {
        lazySource = new Lazy<String>(GetStringFromDatabase);
    }

    public String GetStringFromDatabase()
    {
        return "Hello, Lazy World!";
    }
}

Because following does not compile:

public Lazy<String> LazyInitializeString = new Lazy<String>(() =>
{
    return GetStringFromDatabase();
});

And that property is type of Lazy<String> not String. You you always need to access it's value using LazyInitializeString.Value.

And, I am open for suggestions on how to make it shorter.