public static T GetOrAdd <T>(this MetadataCollection <T> collection, string key, Func <T> factory)
where T : class, IMetadataItem
{
if (!collection.ContainsKey(key))
{
var item = factory();
var writable = collection.GetWritable();
writable[key] = item;
return(item);
}
return(collection[key]);
}
