Is my approach to lazy loading flawed?

Answer 1

Your method is flawed. To take this approach you need to make backingField a ref parameter.

private static T GetProperty<T>(ref T backingField, Func<T> factory)

Then on GetProperty, pass ref _ImagXpress or ref _PdfXpress.

The way you're doing it now just assigns a new value to the parameter, not to the actual backing field.

Answer 2

Your approach is flawed. You're fields will never be set to anything. the backingField argument is being set in the GetProperty<T> method, but this does not update the field you're passing in. You'll want to pass in that argument with the ref keyword attached to it like this:

private static T GetProperty<T>(ref T backingField, Func<T> factory)

Answer 3

To propose a different solution:

I'd say that you're not saving a whole lot by encapsulating that logic into a separate method. You're increasing your complexity without much gain. I'd suggest doing it this way:

protected PdfXpress PdfXpress
{
    get
    {
        if (_PdfXpress == null)
            _PdfXpress = PdfXpressSupport.Create();

        return _PdfXpress;
    }
}

protected ImagXpress ImagXpress
{
    get
    {
        if (_ImagXpress == null)
            _ImagXpress = IMagXpressSupport.Create();

        return _ImagXpress;
    }
}

You're adding a few lines, but decreasing complexity considerably.

Answer 4

As I stated in comments on another answer, the need for a ref parameter is a code smell. First of all, if you're doing this in a method, you're breaking the single responsibility principle, but more importantly, the code is only reusable within your inheritance heirarchy.

There's a pattern to be derived here:

public class LazyInit<T>
    where T : class
{
    private readonly Func<T> _creationMethod;
    private readonly object syncRoot;
    private T _instance;

    [DebuggerHidden]
    private LazyInit()
    {
        syncRoot = new object();
    }

    [DebuggerHidden]
    public LazyInit(Func<T> creationMethod)
        : this()
    {
        _creationMethod = creationMethod;
    }

    public T Instance
    {
        [DebuggerHidden]
        get
        {
            lock (syncRoot)
            {
                if (_instance == null)
                    _instance = _creationMethod();
                return _instance;
            }
        }
    }

    public static LazyInit<T> Create<U>() where U : class, T, new()
    {
        return new LazyInit<T>(() => new U());
    }

    [DebuggerHidden]
    public static implicit operator LazyInit<T>(Func<T> function)
    {
        return new LazyInit<T>(function);
    }
}

This allows you to do this:

public class Foo
{
    private readonly LazyInit<Bar> _bar1 = LazyInit<Bar>.Create<Bar>();
    private readonly LazyInit<Bar> _bar2 = new LazyInit<Bar>(() => new Bar("foo"));

    public Bar Bar1
    {
        get { return _bar1.Instance; }
    }

    public Bar Bar2
    {
        get { return _bar2.Instance; }
    }
}