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Equivalence.java
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53 lines (40 loc) · 1.36 KB
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package testsupport.traits;
import com.jnape.palatable.lambda.functions.Fn1;
import java.util.Objects;
import static com.jnape.palatable.lambda.functions.builtin.fn1.Constantly.constantly;
public final class Equivalence<A> {
private final A value;
private final Fn1<? super A, Object> eq;
private Equivalence(A value, Fn1<? super A, Object> eq) {
this.value = value;
this.eq = eq;
}
public A getValue() {
return value;
}
public Equivalence<A> swap(A a) {
return invMap(constantly(a));
}
public Equivalence<A> invMap(Fn1<? super A, ? extends A> equivalence) {
return new Equivalence<>(value, equivalence.fmap(this.eq));
}
@Override
public String toString() {
return value.getClass().getSimpleName() + " (surrogate)";
}
@Override
public int hashCode() {
return value.hashCode();
}
@Override
public boolean equals(Object obj) {
if (obj instanceof Equivalence) {
@SuppressWarnings("unchecked") Equivalence<A> other = (Equivalence<A>) obj;
return Objects.equals(eq.apply(value), other.eq.apply(other.value));
}
return false;
}
public static <A> Equivalence<A> equivalence(A value, Fn1<? super A, Object> equivalence) {
return new Equivalence<>(value, equivalence);
}
}