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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> {
/**
* List of queued actions to be performed on realized values
*/
private FunctionalList<Function<T, T>> actions;
/**
* The value internally held by this lazy holder
*/
private T held;
/**
* The source for a value held by this lazy holder
*/
private Supplier<T> heldSrc;
/**
* Create a new lazy holder with the given supplier
*
* @param src
* The supplier for a value when it is neededs
*/
public LazyHolder(Supplier<T> src) {
heldSrc = src;
held = null;
}
/**
* Create a new lazy holder with the given value
*
* @param val
* The value held in the holder
*/
public LazyHolder(T val) {
held = val;
}
@Override
public void doWith(Consumer<T> f) {
transform((val) -> {
f.accept(val);
return val;
});
}
@Override
public <NewT> IHolder<NewT> map(Function<T, NewT> f) {
return new LazyHolder<>(() -> {
if (held == null) {
return actions.reduceAux(heldSrc.get(),
Function<T, T>::apply, f::apply);
} else {
return actions.reduceAux(held, Function<T, T>::apply,
f::apply);
}
});
}
@Override
public IHolder<T> transform(Function<T, T> f) {
actions.add(f);
return this;
}
@Override
public <E> E unwrap(Function<T, E> f) {
// Actualize ourselves
if (held == null) {
held = heldSrc.get();
}
actions.forEach((act) -> held = act.apply(held));
return f.apply(held);
}
}
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