com.spotify.mobius.Next Maven / Gradle / Ivy
/*
* -\-\-
* Mobius
* --
* Copyright (c) 2017-2018 Spotify AB
* --
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* -/-/-
*/
package com.spotify.mobius;
import static com.spotify.mobius.internal_util.Preconditions.checkNotNull;
import com.google.auto.value.AutoValue;
import com.spotify.mobius.functions.Consumer;
import com.spotify.mobius.internal_util.ImmutableUtil;
import java.util.NoSuchElementException;
import java.util.Set;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
/**
* This class represents the result of calling an {@link Update} function.
*
* Upon calling an Update function with an Event and Model, a Next object will be returned that
* contains the new Model (if there is one) and Effect objects that describe which side-effects
* should take place.
*/
@AutoValue
public abstract class Next {
protected Next() {}
/** Get the model of this Next, if it has one. Might return null. */
@Nullable
protected abstract M model();
/** Check if this Next contains a model. */
public final boolean hasModel() {
return model() != null;
}
/**
* Get the effects of this Next.
*
* Will return an empty set if there are no effects.
*/
@Nonnull
public abstract Set effects();
/** Check if this Next contains effects. */
public final boolean hasEffects() {
return !effects().isEmpty();
}
/**
* Try to get the model from this Next, with a fallback if there isn't one.
*
* @param fallbackModel the default model to use if the Next doesn't have a model
*/
@Nonnull
public M modelOrElse(M fallbackModel) {
checkNotNull(fallbackModel);
if (hasModel()) {
return modelUnsafe();
} else {
return fallbackModel;
}
}
/**
* Get the model of this Next. This version is unsafe - if this next doesn't have a model, calling
* this method will cause an exception to be thrown.
*
* In almost all cases you should use {@link #modelOrElse} or {@link #ifHasModel} instead.
*
* @throws NoSuchElementException if this Next has no model
*/
@Nonnull
public M modelUnsafe() {
if (!hasModel()) {
throw new NoSuchElementException("there is no model in this Next<>");
}
// we know model is never null here since we just checked it.
//noinspection ConstantConditions
return model();
}
/** If the model is present, call the given consumer with it, otherwise do nothing. */
public void ifHasModel(Consumer consumer) {
checkNotNull(consumer);
if (hasModel()) {
consumer.accept(modelUnsafe());
}
}
////////////////////////////////////////////////////////////////////////////////////////////////
/** Create a Next that updates the model and dispatches the supplied set of effects. */
@Nonnull
public static Next next(M model, Set effects) {
return new AutoValue_Next<>(model, ImmutableUtil.immutableSet(effects));
}
/** Create a Next that updates the model but dispatches no effects. */
@Nonnull
public static Next next(M model) {
return new AutoValue_Next<>(model, ImmutableUtil.emptySet());
}
/** Create a Next that doesn't update the model but dispatches the supplied effects. */
@Nonnull
public static Next dispatch(Set effects) {
return new AutoValue_Next<>(null, ImmutableUtil.immutableSet(effects));
}
/** Create an empty Next that doesn't update the model or dispatch effects. */
@Nonnull
public static Next noChange() {
return new AutoValue_Next<>(null, ImmutableUtil.emptySet());
}
}