How to remove repetitive code that differ in using properties/fields for displaying themselves as strings?

Question

I have two extension methods that are very similar. I'd like to remove the code duplicates with «the hole in the middle» pattern or the like, but can't really get it to work.

The code looks like so:

public static String GetPublicPropertiesAsString( this Object @this )
{
    return @this.GetType().GetProperties()
        .Select( propertyInfo =>
                        {
                            var propertyValue = propertyInfo.GetValue( obj: @this,
                                                                    invokeAttr: BindingFlags.Public,
                                                                    binder: null,
                                                                    index: null,
                                                                    culture: null );

                            var propertyValueAsString = propertyValue != null ? propertyValue.ToString().RemoveAll( "00:00:00" ) : "[null]";

                            return "{0}: {1}".FormatWith( propertyInfo.Name, propertyValueAsString );
                        } ).JoinAsString( Environment.NewLine );
}

public static String GetFieldsAsString( this Object @this )
{
    return @this.GetType().GetFields()
        .Select( fieldInfo =>
                        {
                            var fieldValue = fieldInfo.GetValue( @this );

                            var fieldValueAsString = fieldValue != null ? fieldValue.ToString().RemoveAll( "00:00:00" ) : "[null]";

                            return "{0}: {1}".FormatWith( fieldInfo.Name, fieldValueAsString );
                        } ).JoinAsString( Environment.NewLine );
}

Could the repetitive code above be refactored away?

Note: JoinAsString, RemoveAll, and FormatWith are my own extension methods.

Answer 1

I would refactor that middle code out to a single method that accepts MemberInfo[], and does a switch on the member type. Untested, but:

    private static string GetMembersAsString(object @this, MemberInfo[] members)
    {
        var sb = new StringBuilder();
        for (int i = 0; i < members.Length; i++)
        {
            var member = members[i];
            if (i != 0) sb.AppendLine();
            object value;
            switch(member.MemberType) {
                case MemberTypes.Field:
                    value = ((FieldInfo)member).GetValue(@this);
                    break;
                case MemberTypes.Property:
                    value = ((PropertyInfo)member).GetValue(@this, null);
                    break;
                default:
                    throw new NotSupportedException(member.MemberType.ToString());
            }
            string s = value == null ? "[null]" : value.ToString().RemoveAll("00:00:00");
            sb.Append(member.Name).Append(" = ").Append(s);
        }
        return sb.ToString();
    }
    public static String GetPublicPropertiesAsString(this Object @this)
    {
        return GetMembersAsString(@this, @this.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance));
    }

    public static String GetFieldsAsString(this Object @this)
    {
        return GetMembersAsString(@this, @this.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance));
    }

Answer 2

Yes, it can. By using generics and the fact that both PropertyInfo and FieldInfo derives from MemberInfo.

Something like this:

static string GetAsString<T>
    (object @this, Func<T, object> getter) where T : MemberInfo
{
  return @this.GetType().GetMembers(/* binding flags */).OfType<T>().Select(
    x => 
    {
      var value = getter(x);
      var valueAsString = value != null ? value.ToString().
           RemoveAll( "00:00:00" ) : "[null]";
      return "{0}: {1}".FormatWith( x.Name, valueAsString );
    }).JoinAsString();
}

Now the hook up:

public static String GetPublicPropertiesAsString( this Object @this )
{
  return GetAsString<PropertyInfo>(@this, x => x.GetValue(@this, null));
}

public static String GetPublicFieldsAsString( this Object @this )
{
  return GetAsString<FieldInfo>(@this, x => x.GetValue(@this));
}