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package bjc.data;
import java.util.function.BiFunction;
import java.util.function.Function;
/**
* Represents a pair where only one side has a value.
*
* @author ben
*
* @param <LeftType>
* The type that could be on the left.
*
* @param <RightType>
* The type that could be on the right.
*
*/
public class Either<LeftType, RightType> implements Pair<LeftType, RightType> {
/**
* Create a new either with the left value occupied.
*
* @param <LeftType>
* The type of the left value.
*
* @param <RightType>
* The type of the empty right value.
*
* @param left
* The value to put on the left.
*
* @return An either with the left side occupied.
*/
public static <LeftType, RightType> Either<LeftType, RightType>
left(final LeftType left) {
return new Either<>(left, null);
}
/**
* Create a new either with the right value occupied.
*
* @param <LeftType>
* The type of the empty left value.
*
* @param <RightType>
* The type of the right value.
*
* @param right
* The value to put on the right.
*
* @return An either with the right side occupied.
*/
public static <LeftType, RightType> Either<LeftType, RightType>
right(final RightType right) {
return new Either<>(null, right);
}
/* The left value of the either. */
private LeftType leftVal;
/* The right value of the either. */
private RightType rightVal;
/* Whether the left value is the one filled out. */
private boolean isLeft;
/* Create a new either with specifed values. */
private Either(final LeftType left, final RightType right) {
if (left == null) {
rightVal = right;
} else {
leftVal = left;
isLeft = true;
}
}
@Override
public <BoundLeft, BoundRight> Pair<BoundLeft, BoundRight> bind(
final BiFunction<LeftType, RightType, Pair<BoundLeft, BoundRight>> binder) {
if (binder == null) throw new NullPointerException("Binder must not be null");
return binder.apply(leftVal, rightVal);
}
@Override
public <BoundLeft> Pair<BoundLeft, RightType>
bindLeft(final Function<LeftType, Pair<BoundLeft, RightType>> leftBinder) {
if (leftBinder == null) throw new NullPointerException("Left binder must not be null");
if (isLeft) return leftBinder.apply(leftVal);
else return new Either<>(null, rightVal);
}
@Override
public <BoundRight> Pair<LeftType, BoundRight> bindRight(
final Function<RightType, Pair<LeftType, BoundRight>> rightBinder) {
if (rightBinder == null) throw new NullPointerException("Right binder must not be null");
if (isLeft) return new Either<>(leftVal, null);
else return rightBinder.apply(rightVal);
}
@Override
public <OtherLeft, OtherRight, CombinedLeft, CombinedRight>
Pair<CombinedLeft, CombinedRight>
combine(final Pair<OtherLeft, OtherRight> otherPair,
final BiFunction<LeftType, OtherLeft, CombinedLeft> leftCombiner,
final BiFunction<RightType, OtherRight,
CombinedRight> rightCombiner) {
if (otherPair == null) {
throw new NullPointerException("Other pair must not be null");
} else if (leftCombiner == null) {
throw new NullPointerException("Left combiner must not be null");
} else if (rightCombiner == null) {
throw new NullPointerException("Right combiner must not be null");
}
if (isLeft) {
return otherPair.bind((otherLeft, otherRight) -> {
CombinedLeft cLeft = leftCombiner.apply(leftVal, otherLeft);
return new Either<>(cLeft, null);
});
} else {
return otherPair.bind((otherLeft, otherRight) -> {
CombinedRight cRight = rightCombiner.apply(rightVal, otherRight);
return new Either<>(null, cRight);
});
}
}
@Override
public <NewLeft> Pair<NewLeft, RightType>
mapLeft(final Function<LeftType, NewLeft> mapper) {
if (mapper == null) throw new NullPointerException("Mapper must not be null");
if (isLeft) return new Either<>(mapper.apply(leftVal), null);
else return new Either<>(null, rightVal);
}
@Override
public <NewRight> Pair<LeftType, NewRight>
mapRight(final Function<RightType, NewRight> mapper) {
if (mapper == null) throw new NullPointerException("Mapper must not be null");
if (isLeft) return new Either<>(leftVal, null);
else return new Either<>(null, mapper.apply(rightVal));
}
@Override
public <MergedType> MergedType
merge(final BiFunction<LeftType, RightType, MergedType> merger) {
if (merger == null) throw new NullPointerException("Merger must not be null");
return merger.apply(leftVal, rightVal);
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + (isLeft ? 1231 : 1237);
result = prime * result + (leftVal == null ? 0 : leftVal.hashCode());
result = prime * result + (rightVal == null ? 0 : rightVal.hashCode());
return result;
}
@Override
public boolean equals(final Object obj) {
if (this == obj) return true;
if (obj == null) return false;
if (!(obj instanceof Either<?, ?>)) return false;
final Either<?, ?> other = (Either<?, ?>) obj;
if (isLeft != other.isLeft) return false;
if (leftVal == null) {
if (other.leftVal != null) return false;
} else if (!leftVal.equals(other.leftVal)) {
return false;
}
if (rightVal == null) {
if (other.rightVal != null) return false;
} else if (!rightVal.equals(other.rightVal)) {
return false;
}
return true;
}
@Override
public String toString() {
return String.format("Either [leftVal='%s', rightVal='%s', isLeft=%s]", leftVal,
rightVal, isLeft);
}
}
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