A key that takes its identity from the object used as its value.
Used to tie the identity of a widget to the identity of an object used to
generate that widget.
See also the discussions at Key and Widget.key.
Creates a key that uses
value for its operator==.
The hash code for this object. [...]
The object whose identity is used by this key's
A representation of the runtime type of the object.
Returns a string representation of this object.
Invoked when a non-existent method or property is accessed. [...]