Elegant way to avoid NullReferenceException in C#

Question

I want to do this

var path = HttpContext.Current.Request.ApplicationPath;

If any of the Properties along the way is null, i want path to be

Answer 1

UPDATE (November 2014)

C# 6 contains something called the Null Propagation Operator, which means that there is language support for this. Your example can be written as follows in C# 6:

var path = HttpContext?.Current?.Request?.ApplicationPath;

If any of the parts contains null, the complete expression will return null.

---

You can write something like this:

string value = NullHelpers.GetValueOrNull(
    () => HttpContext.Current.Request.ApplicationPath);

The simplest way to implement this NullHelpers.GetValueOrNull is probably something like this:

public static T GetValueOrNull(Func valueProvider) 
    where T : class
{
    try
    {
        return valueProvider();
    }
    catch (NullReferenceException)
    {
        return null;
    }
}

But by far the coolest way to solve this is by using Expression trees:

public static T GetValueOrNull(
    Expression> valueProvider) 
    where T : class
{
    var expression = (MemberExpression)
        ((MemberExpression)valueProvider.Body).Expression;

    var members = new List();

    while (expression != null)
    {
        members.Add(expression);

        expression = 
            (MemberExpression)expression.Expression;
    }

    members.Reverse();

    foreach (var member in members)
    {
        var func = Expression.Lambda>(member).Compile();

        if (func() == null)
        {
            return null;
        }
    }

    return valueProvider.Compile()();
}

This is also the slowest way to do things, since each call will do one or multiple JIT compiler invocations, but...

It is still cool ;-)