# cirq.value_equality¶

cirq.value_equality(cls: type = None, *, unhashable: bool = False, distinct_child_types: bool = False, manual_cls: bool = False, approximate: bool = False) → Union[Callable[type, type], type][source]

Implements eq/ne/hash via a value_equality_values method.

value_equality_values is a method that the decorated class must implement.

value_equality_approximate_values is a method that the decorated class
might implement if special support for approximate equality is required.
This is only used when approximate argument is set. When approximate
argument is set and value_equality_approximate_values is not defined,
value_equality_values values are used for approximate equality.
For example, this can be used to compare periodic values like angles: the
angle value can be wrapped with PeriodicValue. When returned as part of
approximate values a special normalization will be done automatically to
guarantee correctness.
Note that the type of the decorated value is included as part of the value
equality values. This is so that completely separate classes with identical
equality values (e.g. a Point2D and a Vector2D) don’t compare as equal.
Further note that this means that child types of the decorated type will be
considered equal to each other, though this behavior can be changed via
the ‘distinct_child_typesargument. The type logic is implemented behind the scenes by avalue_equality_values_cls` method added to the class.
Parameters
• cls – The type to decorate. Automatically passed in by python when using the @cirq.value_equality decorator notation on a class.

• unhashable – When set, the __hash__ method will be set to None instead of to a hash of the equality class and equality values. Useful for mutable types such as dictionaries.

• distinct_child_types – When set, classes that inherit from the decorated class will not be considered equal to it. Also, different child classes will not be considered equal to each other. Useful for when the decorated class is an abstract class or trait that is helping to define equality for many conceptually distinct concrete classes.

• manual_cls – When set, the method ‘_value_equality_values_cls_’ must be implemented. This allows a new class to compare as equal to another existing class that is also using value equality, by having the new class return the existing class’ type. Incompatible with distinct_child_types.

• approximate – When set, the decorated class will be enhanced with _approx_eq_ implementation and thus start to support the SupportsApproximateEquality protocol.