Can I get specific metadata from a Func?

Question

Consider the following code:

string propertyName;
var dateList = new List() { DateTime.Now };
propertyName = dateList.GetPropertyName(dateTimeObj         


        

Answer 1

This is the version I use, it returns a PropertyInfo, but getting the name is trivial.

public static PropertyInfo GetProperty<T>(Expression<Func<T, object>> expression)  
{
    MemberExpression memberExpression = null;

    if (expression.Body.NodeType == ExpressionType.Convert)
    {
        memberExpression = ((UnaryExpression) expression.Body).Operand as MemberExpression;
    }
    else if (expression.Body.NodeType == ExpressionType.MemberAccess)
    {
        memberExpression = expression.Body as MemberExpression;
    }

    if (memberExpression == null)
    {
        throw new ArgumentException("Not a member access", "expression");
    }

    return memberExpression.Member as PropertyInfo;
}

Answer 2

Something like this should do the trick:

public static string GetPropertyName<T>(this IList<T> list, Expression<Func<T, object>> expr) {
  MemberExpression member_expression = expr.Body as MemberExpression;
  if (member_expression == null)
      throw new ArgumentNullException("member_expression");
  MemberInfo member = member_expression.Member;
  PropertyInfo property = member as PropertyInfo;
  string proname = memeber.name;
}

WARNING: Air Code!

Answer 3

here is a very easy and fast way to do it on this blog: http://blog.bittercoder.com/PermaLink,guid,206e64d1-29ae-4362-874b-83f5b103727f.aspx

So given:

Func func = Name => "Value";

You can get the lambda parameter "Name" from the function delegate by calling:

func.Method.GetParameters()[0].Name (would return "Name")

Here's the revised Hash method from Andrey:

public Dictionary<string, T> Hash<T>(params Func<string, T>[] args)
where T : class
{
    var items = new Dictionary<string, T>();
    foreach (var func in args)
    {
        var item = func(null);
        items.Add(func.Method.GetParameters()[0].Name, item);
    }
    return items;
}

Hope it helps, Patrick

Answer 4

Just a side note: func.Method.GetParameters()[0].Name is extremelly fast when compared with compiling the lambda and extracting the member expression, then the member info, then the name.