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/*
* esodata - data structures and other things, of varying utility
* Copyright 2022, Ben Culkin
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
package bjc.data.internals;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.function.UnaryOperator;
import bjc.data.Holder;
import bjc.data.Lazy;
import bjc.funcdata.FunctionalList;
import bjc.funcdata.ListEx;
/**
* Implements a lazy holder that has been bound.
*
* @author Ben Culkin
* @param <OldType>
* The old type of the value.
* @param <BoundContainedType>
* The type of the new bound value.
*/
public class BoundLazy<OldType, BoundContainedType>
implements Holder<BoundContainedType> {
/* The old value. */
private final Supplier<Holder<OldType>> oldSupplier;
/* The function to use to transform the old value into a new value. */
private final Function<OldType, Holder<BoundContainedType>> binder;
/* The bound value being held. */
private Holder<BoundContainedType> boundHolder;
/* Whether the bound value has been actualized or not. */
private boolean holderBound;
/* Transformations currently pending on the bound value. */
private final ListEx<UnaryOperator<BoundContainedType>> actions
= new FunctionalList<>();
/**
* Create a new bound lazy value.
*
* @param supp
* The supplier of the old value.
*
* @param binder
* The function to use to bind the old value to the new one.
*/
public BoundLazy(final Supplier<Holder<OldType>> supp,
final Function<OldType, Holder<BoundContainedType>> binder) {
oldSupplier = supp;
this.binder = binder;
}
@Override
public <BoundType> Holder<BoundType>
bind(final Function<BoundContainedType, Holder<BoundType>> bindr) {
if (bindr == null)
throw new NullPointerException("Binder must not be null");
/* Prepare a list of pending actions. */
final ListEx<UnaryOperator<BoundContainedType>> pendingActions
= new FunctionalList<>();
for (UnaryOperator<BoundContainedType> pendAct : actions) {
pendingActions.add(pendAct);
}
/* Create the new supplier of a value. */
final Supplier<Holder<BoundContainedType>> typeSupplier = () -> {
Holder<BoundContainedType> oldHolder = boundHolder;
/* Bind the value if it hasn't been bound before. */
if (!holderBound) {
oldHolder = oldSupplier.get().unwrap(binder);
}
/* Apply all the pending actions. */
return pendingActions.reduceAux(oldHolder,
(action, state) -> state.transform(action), value -> value);
};
return new BoundLazy<>(typeSupplier, bindr);
}
@Override
public <NewType> Function<BoundContainedType, Holder<NewType>>
lift(final Function<BoundContainedType, NewType> func) {
if (func == null)
throw new NullPointerException("Function to lift must not be null");
return val -> {
return new Lazy<>(func.apply(val));
};
}
@Override
public <MappedType> Holder<MappedType>
map(final Function<BoundContainedType, MappedType> mapper) {
if (mapper == null)
throw new NullPointerException("Mapper must not be null");
/* Prepare a list of pending actions. */
final ListEx<UnaryOperator<BoundContainedType>> pendingActions
= new FunctionalList<>();
for (UnaryOperator<BoundContainedType> pendAct : actions) {
pendingActions.add(pendAct);
}
/* Prepare the new supplier. */
final Supplier<MappedType> typeSupplier = () -> {
Holder<BoundContainedType> oldHolder = boundHolder;
/* Bound the value if it hasn't been bound. */
if (!holderBound) {
oldHolder = oldSupplier.get().unwrap(binder);
}
/* Apply pending actions. */
return pendingActions.reduceAux(oldHolder.getValue(),
(action, state) -> action.apply(state), value -> mapper.apply(value));
};
return new Lazy<>(typeSupplier);
}
@Override
public String toString() {
if (holderBound)
return boundHolder.toString();
return "(unmaterialized)";
}
@Override
public Holder<BoundContainedType>
transform(final UnaryOperator<BoundContainedType> transformer) {
if (transformer == null)
throw new NullPointerException("Transformer must not be null");
actions.add(transformer);
return this;
}
@Override
public <UnwrappedType> UnwrappedType
unwrap(final Function<BoundContainedType, UnwrappedType> unwrapper) {
if (unwrapper == null)
throw new NullPointerException("Unwrapper must not be null");
if (!holderBound) {
boundHolder = oldSupplier.get().unwrap(binder::apply);
}
return boundHolder.unwrap(unwrapper);
}
}
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