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package bjc.utils.data.lazy;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;
import bjc.utils.data.IHolder;
import bjc.utils.funcdata.FunctionalList;
/**
* Holds a single value of a specific type. This is used for indirect
* references to data, and more specifically for accessing non-final
* variables from a lambda. AKA the identity monad
*
* This is a lazy variant of {@link IHolder}
*
* @author ben
*
* @param <T>
* The type of the data being held
*/
public class LazyHolder<T> implements IHolder<T> {
private final class LazyHolderSupplier<NewT>
implements Supplier<NewT> {
private FunctionalList<Function<T, T>> pendingActions;
private Function<T, NewT> pendingTransform;
public LazyHolderSupplier(FunctionalList<Function<T, T>> actons,
Function<T, NewT> transform) {
// Resolve latent bug I just realized. After a map, adding new
// actions to the original holder could've resulted in changes
// to all unactualized mapped values from that holder
pendingActions = actons.clone();
this.pendingTransform = transform;
}
@Override
public NewT get() {
if (heldValue == null) {
return pendingActions.reduceAux(heldSource.get(),
Function<T, T>::apply, pendingTransform::apply);
} else {
return pendingActions.reduceAux(heldValue,
Function<T, T>::apply, pendingTransform::apply);
}
}
}
/**
* List of queued actions to be performed on realized values
*/
private FunctionalList<Function<T, T>> actions =
new FunctionalList<>();
/**
* The value internally held by this lazy holder
*/
private T heldValue;
/**
* The source for a value held by this lazy holder
*/
private Supplier<T> heldSource;
/**
* Create a new lazy holder with the given supplier
*
* @param source
* The supplier for a value when it is neededs
*/
public LazyHolder(Supplier<T> source) {
heldSource = source;
heldValue = null;
}
/**
* Create a new lazy holder with the given value
*
* @param value
* The value held in the holder
*/
public LazyHolder(T value) {
heldValue = value;
}
@Override
public void doWith(Consumer<T> action) {
transform((value) -> {
// Do the action with the value
action.accept(value);
// Return the untransformed value
return value;
});
}
@Override
public <NewT> IHolder<NewT> map(Function<T, NewT> transform) {
// Don't actually map until we need to
return new LazyHolder<>(
new LazyHolderSupplier<>(actions, transform));
}
@Override
public IHolder<T> transform(Function<T, T> transform) {
// Queue the transform until we need to apply it
actions.add(transform);
return this;
}
@Override
public <E> E unwrap(Function<T, E> unwrapper) {
// Actualize ourselves
if (heldValue == null) {
heldValue = heldSource.get();
}
// Apply all pending transforms
actions.forEach((action) -> heldValue = action.apply(heldValue));
return unwrapper.apply(heldValue);
}
}
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