class ContextConc implements Context {

  @SuppressWarnings("unchecked")
  @Override
  public <T> T get(final Key<T> key) {
    assertNotNull(key, "Key must not null");
    final T value = (T) key2Value.get(key);
    return value;
  }

   <T> ContextConc(final Context parent, final String scope);
   <T> ContextConc(final Context parent, final Key<T> key, final T value);

}