contramap<A> method

Eq<A> contramap<A>(T map(A))

Return an Eq instance based on a parameter of type T extracted from a class A.

class Parent {
  final int value1;
  final double value2;
  const Parent(this.value1, this.value2);
}
/// Equality for values of type [Parent] based on their `value1` ([int]).
final eqParentInt = Eq.eqInt.contramap<Parent>(
  (p) => p.value1,
);
/// Equality for of type [Parent] based on their `value2` ([double]).
final eqParentDouble = Eq.eqDouble.contramap<Parent>(
  (p) => p.value2,
);

Implementation

/// /// Equality for values of type [Parent] based on their `value1` ([int]).
/// final eqParentInt = Eq.eqInt.contramap<Parent>(
///   (p) => p.value1,
/// );

/// /// Equality for of type [Parent] based on their `value2` ([double]).
/// final eqParentDouble = Eq.eqDouble.contramap<Parent>(
///   (p) => p.value2,
/// );
/// ```
Eq<A> contramap<A>(T Function(A) map) => _Eq<A>(
      (a1, a2) => eqv(map(a1), map(a2)),
    );