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package bjc.utils.data;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;
/**
* A lazy implementation of a pair
*
* @author ben
*
* @param <LeftType>
* The type on the left side of the pair
* @param <RightType>
* The type on the right side of the pair
*/
public class LazyPair<LeftType, RightType>
implements IPair<LeftType, RightType> {
private LeftType leftValue;
private RightType rightValue;
private Supplier<LeftType> leftSupplier;
private Supplier<RightType> rightSupplier;
private boolean leftMaterialized;
private boolean rightMaterialized;
/**
* Create a new lazy pair, using the set value s
*
* @param leftVal
* The value for the left side of the pair
* @param rightVal
* The value for the right side of the pair
*/
public LazyPair(LeftType leftVal, RightType rightVal) {
leftValue = leftVal;
rightValue = rightVal;
leftMaterialized = true;
rightMaterialized = true;
}
/**
* Create a new lazy pair from the given value sources
*
* @param leftSupp
* The source for a value on the left side of the pair
* @param rightSupp
* The source for a value on the right side of the pair
*/
public LazyPair(Supplier<LeftType> leftSupp,
Supplier<RightType> rightSupp) {
leftSupplier = leftSupp;
rightSupplier = rightSupp;
leftMaterialized = false;
rightMaterialized = false;
}
@Override
public <BoundLeft, BoundRight> IPair<BoundLeft, BoundRight> bind(
BiFunction<LeftType, RightType, IPair<BoundLeft, BoundRight>> binder) {
return new BoundLazyPair<>(leftSupplier, rightSupplier, binder);
}
@Override
public <BoundLeft> IPair<BoundLeft, RightType> bindLeft(
Function<LeftType, IPair<BoundLeft, RightType>> leftBinder) {
Supplier<LeftType> leftSupp = () -> {
if (leftMaterialized) {
return leftValue;
}
return leftSupplier.get();
};
return new HalfBoundLazyPair<>(leftSupp, leftBinder);
}
@Override
public <BoundRight> IPair<LeftType, BoundRight> bindRight(
Function<RightType, IPair<LeftType, BoundRight>> rightBinder) {
Supplier<RightType> rightSupp = () -> {
if (rightMaterialized) {
return rightValue;
}
return rightSupplier.get();
};
return new HalfBoundLazyPair<>(rightSupp, rightBinder);
}
@Override
public LeftType getLeft() {
if (!leftMaterialized) {
leftValue = leftSupplier.get();
leftMaterialized = true;
}
return leftValue;
}
@Override
public RightType getRight() {
if (!rightMaterialized) {
rightValue = rightSupplier.get();
rightMaterialized = true;
}
return rightValue;
}
@Override
public <MergedType> MergedType merge(
BiFunction<LeftType, RightType, MergedType> merger) {
if (!leftMaterialized) {
leftValue = leftSupplier.get();
leftMaterialized = true;
}
if (!rightMaterialized) {
rightValue = rightSupplier.get();
rightMaterialized = true;
}
return merger.apply(leftValue, rightValue);
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder("pair[l=");
if (leftMaterialized) {
sb.append(leftValue.toString());
} else {
sb.append("(un-materialized)");
}
sb.append(", r=");
if (rightMaterialized) {
sb.append(rightValue.toString());
} else {
sb.append("(un-materialized)");
}
sb.append("]");
return sb.toString();
}
}
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