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// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jdisc.http.server.jetty;
import java.util.Objects;
import java.util.function.Supplier;
/**
* Simple monad class, like Optional but with support for chaining alternatives in preferred order.
*
* Holds a current value (immutably), but if the current value is null provides an easy way to obtain an instance
* with another value, ad infinitum.
*
* Instances of this class are immutable and thread-safe.
*
* @author bakksjo
*/
public class Alternative<T> {
private final T value;
private Alternative(final T value) {
this.value = value;
}
/**
* Creates an instance with the supplied value.
*/
public static <T> Alternative<T> preferred(final T value) {
return new Alternative<>(value);
}
/**
* Returns itself (unchanged) iff current value != null,
* otherwise returns a new instance with the value supplied by the supplier.
*/
public Alternative<T> alternatively(final Supplier<? extends T> supplier) {
if (value != null) {
return this;
}
return new Alternative<>(supplier.get());
}
/**
* Returns the held value iff != null, otherwise invokes the supplier and returns its value.
*/
public T orElseGet(final Supplier<? extends T> supplier) {
if (value != null) {
return value;
}
return supplier.get();
}
@Override
public boolean equals(final Object o) {
if (!(o instanceof Alternative<?>)) {
return false;
}
final Alternative<?> other = (Alternative<?>) o;
return Objects.equals(value, other.value);
}
@Override
public int hashCode() {
return Objects.hashCode(value);
}
}
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