@EqualsAndHashCode#

Generates __eq__ and __hash__ together.

The problem it solves#

By default two instances are equal only if they are the same object. For a value-like class you usually want value equality — equal if all fields are equal — and a matching __hash__ so instances can live in sets and dict keys. Python couples the two (defining __eq__ without __hash__ makes a class unhashable), which is easy to get wrong by hand. @EqualsAndHashCode generates both, consistently, from the class’s fields — without a constructor or repr.

Usage#

from inito import EqualsAndHashCode


@EqualsAndHashCode
class Version:
    major: int
    minor: int


a, b = Version(), Version()
a.major, a.minor = 1, 4
b.major, b.minor = 1, 4
print(a == b)             # True  (value equality)
print(hash(a) == hash(b)) # True
print({a, b})             # a single-element set — a and b are equal & hash equal

What it generates#

Member	Behaviour
`__eq__`	compares the tuple of all field values; a different class yields `NotImplemented`
`__hash__`	`hash()` of the tuple of all field values

The two are always generated together — matching Lombok’s equals()/hashCode() pairing and Python’s own hash/eq contract.

Options#

None today; @EqualsAndHashCode and @EqualsAndHashCode() are equivalent.

Notes & gotchas#

Equality is class-exact: a == b is only considered when a.__class__ is b.__class__, otherwise it returns NotImplemented (so a subclass and base instance are never accidentally “equal”).
Because it generates __hash__, instances stay hashable even though they are mutable — the hash reflects the current field values, so avoid mutating an instance while it is stored in a set or used as a dict key.