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package bjc.data;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.function.UnaryOperator;
import bjc.data.internals.BoundLazy;
import bjc.funcdata.FunctionalList;
import bjc.funcdata.IList;
/**
* A holder that holds a means to create a value, but doesn't actually compute
* the value until it's needed.
*
* @author ben
*
* @param <ContainedType>
* The type of the value being held.
*/
public class Lazy<ContainedType> implements IHolder<ContainedType> {
/* The supplier of the type. */
private Supplier<ContainedType> valueSupplier;
/* The actual type value. */
private ContainedType heldValue;
/* Whether the value has been created. */
private boolean valueMaterialized;
/* The list of pending actions on the value. */
private IList<UnaryOperator<ContainedType>> actions = new FunctionalList<>();
/**
* Create a new lazy value from the specified seed value.
*
* @param value
* The seed value to use.
*/
public Lazy(final ContainedType value) {
heldValue = value;
valueMaterialized = true;
}
/**
* Create a new lazy value from the specified value source.
*
* @param supp
* The source of a value to use.
*/
public Lazy(final Supplier<ContainedType> supp) {
valueSupplier = new SingleSupplier<>(supp);
valueMaterialized = false;
}
/* Create a new value from a supplier and a list of actions. */
private Lazy(final Supplier<ContainedType> supp,
final IList<UnaryOperator<ContainedType>> pendingActions) {
valueSupplier = supp;
actions = pendingActions;
}
@Override
public <BoundType> IHolder<BoundType>
bind(final Function<ContainedType, IHolder<BoundType>> binder) {
final IList<UnaryOperator<ContainedType>> pendingActions = new FunctionalList<>();
actions.forEach(pendingActions::add);
final Supplier<ContainedType> supplier = () -> {
if (valueMaterialized)
return heldValue;
return valueSupplier.get();
};
return new BoundLazy<>(() -> new Lazy<>(supplier, pendingActions), binder);
}
@Override
public <NewType> Function<ContainedType, IHolder<NewType>>
lift(final Function<ContainedType, NewType> func) {
return val -> new Lazy<>(func.apply(val));
}
@Override
public <MappedType> IHolder<MappedType>
map(final Function<ContainedType, MappedType> mapper) {
final IList<UnaryOperator<ContainedType>> pendingActions = new FunctionalList<>();
actions.forEach(pendingActions::add);
return new Lazy<>(() -> {
ContainedType currVal = heldValue;
if (!valueMaterialized) {
currVal = valueSupplier.get();
}
return pendingActions.reduceAux(currVal, UnaryOperator<ContainedType>::apply,
value -> mapper.apply(value));
});
}
@Override
public String toString() {
if (valueMaterialized) {
if (actions.isEmpty()) {
return String.format("value[v='%s']", heldValue);
}
return String.format("value[v='%s'] (has pending transforms)", heldValue);
}
return "(unmaterialized)";
}
@Override
public IHolder<ContainedType>
transform(final UnaryOperator<ContainedType> transformer) {
actions.add(transformer);
return this;
}
@Override
public <UnwrappedType> UnwrappedType
unwrap(final Function<ContainedType, UnwrappedType> unwrapper) {
if (!valueMaterialized) {
heldValue = valueSupplier.get();
valueMaterialized = true;
}
actions.forEach(action -> {
heldValue = action.apply(heldValue);
});
actions = new FunctionalList<>();
return unwrapper.apply(heldValue);
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + (actions == null ? 0 : actions.hashCode());
result = prime * result + (heldValue == null ? 0 : heldValue.hashCode());
result = prime * result + (valueMaterialized ? 1231 : 1237);
return result;
}
@Override
public boolean equals(final Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (!(obj instanceof Lazy<?>))
return false;
final Lazy<?> other = (Lazy<?>) obj;
if (valueMaterialized != other.valueMaterialized)
return false;
if (valueMaterialized) {
if (heldValue == null) {
if (other.heldValue != null)
return false;
} else if (!heldValue.equals(other.heldValue))
return false;
} else
return false;
if (actions == null) {
if (other.actions != null)
return false;
} else if (actions.getSize() > 0 || other.actions.getSize() > 0)
return false;
return true;
}
/**
* Create a new lazy container with an already present value.
*
* @param val
* The value for the lazy container.
*
* @return A new lazy container holding that value.
*/
public static <ContainedType> Lazy<ContainedType> lazy(final ContainedType val) {
return new Lazy<>(val);
}
/**
* Create a new lazy container with a suspended value.
*
* @param supp
* The suspended value for the lazy container.
*
* @return A new lazy container that will un-suspend the value when necessary.
*/
public static <ContainedType> Lazy<ContainedType>
lazy(final Supplier<ContainedType> supp) {
return new Lazy<>(supp);
}
}
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