Dynamic Programming in C# - Effective C# - page 248

Getting the third planet would be simply using an indexer:
// gets the third planet (Earth)
dynamic test3 = dynamicXML[ "Planet" , 2 ];
Reaching the moons becomes two chained indexers:
dynamic earthMoon = dynamicXML[ "Planet" , 2 ][ "Moons" , 0 ].Moon;
Finally, because it's dynamic, you can define the semantics so any missing
node returns an empty element. That means all of these would return
empty dynamic XElement nodes:
dynamic test6 = dynamicXML[ "Planet" , 2 ]
[ "Moons" , 3 ].Moon; // earth doesn't have 4 moons
dynamic fail = dynamicXML.NotAppearingInThisFile;
dynamic fail2 = dynamicXML.Not.Appearing.In.This.File;
Because missing elements will return a missing dynamic element, you can
continue to dereference it and know that if any element in the composed
XML navigation is missing, the final result will be a missing element.
Building this is another class derived from DynamicObject. You have to
override TryGetMember, and TryGetIndex to return dynamic elements
with the appropriate nodes.
public class DynamicXElement : DynamicObject
{
private readonly XElement xmlSource;
public DynamicXElement( XElement source)
{
xmlSource = source;
}
public override bool TryGetMember( GetMemberBinder binder,
out object result)
{
result = new DynamicXElement ( null );
if (binder.Name == "Value" )
{
result = (xmlSource != null ) ?
xmlSource.Value : "" ;
return true ;
}