/// <summary>
/// Gets the attribute for the given attribute key.
/// This method will never return null, but may return
/// an attribute which does not have a value set yet.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="key"></param>
/// <returns></returns>
public IAttribute <T> Attr <T>(AttributeKey <T> key)
{
if (key == null)
{
throw new NullReferenceException("key");
}
var attributes = _attributes;
if (attributes == null)
{
attributes = new ConcurrentDictionary <AttributeKey, IAttribute>();
// atomically: if _attributes == null -> replace it with attributes
Interlocked.CompareExchange(ref _attributes, attributes, null);
}
var attr = attributes.GetOrAdd(key, new DefaultAttribute <T>(key));
return((IAttribute <T>)attr);
}
internal DefaultAttribute(AttributeKey <T> key)
{
_key = key;
}