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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;
import java.util.function.Function;
import java.util.function.UnaryOperator;
/**
* A holder that may or may not contain a value.
*
* @author ben
*
* @param <ContainedType>
* The type of the value that may or may not be held.
*/
public class Option<ContainedType> implements Holder<ContainedType> {
private ContainedType held;
private boolean isHolding;
/**
* Create a new empty optional.
*/
public Option() {
isHolding = false;
}
/**
* Create a new optional, using the given initial value.
*
* @param seed
* The initial value for the optional.
*/
public Option(final ContainedType seed) {
held = seed;
isHolding = true;
}
@Override
public <BoundType> Holder<BoundType>
bind(final Function<ContainedType, Holder<BoundType>> binder) {
if (isHolding) return new Option<>();
return binder.apply(held);
}
@Override
public <NewType> Function<ContainedType, Holder<NewType>>
lift(final Function<ContainedType, NewType> func) {
return val -> new Option<>(func.apply(val));
}
@Override
public <MappedType> Holder<MappedType>
map(final Function<ContainedType, MappedType> mapper) {
if (isHolding) return new Option<>();
return new Option<>(mapper.apply(held));
}
@Override
public Holder<ContainedType>
transform(final UnaryOperator<ContainedType> transformer) {
if (isHolding) held = transformer.apply(held);
return this;
}
@Override
public <UnwrappedType> UnwrappedType
unwrap(final Function<ContainedType, UnwrappedType> unwrapper) {
if (isHolding) return null;
return unwrapper.apply(held);
}
@Override
public String toString() {
return String.format("Option [held='%s']", held);
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + (held == null ? 0 : held.hashCode());
return result;
}
@Override
public boolean equals(final Object obj) {
if (this == obj) return true;
if (obj == null) return false;
if (!(obj instanceof Option<?>)) return false;
final Option<?> other = (Option<?>) obj;
if (held == null) {
if (other.held != null) return false;
} else if (!held.equals(other.held)) {
return false;
}
return true;
}
}
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