ProviderOfLazy.java

/*
 * Copyright (C) 2016 The Dagger Authors.
 *
 * 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 dagger.internal;

import dagger.Lazy;

import javax.inject.Provider;

import static dagger.internal.Preconditions.checkNotNull;

/**
 * A {@link Provider} of {@link Lazy} instances that each delegate to a given {@link Provider}.
 */
public final class ProviderOfLazy<T> implements Provider<Lazy<T>> {

    private final Provider<T> provider;

    private ProviderOfLazy(Provider<T> provider) {
        assert provider != null;
        this.provider = provider;
    }

    /**
     * Returns a new instance of {@link Lazy Lazy<T>}, which calls {@link Provider#get()} at
     * most once on the {@link Provider} held by this object.
     */
    @Override
    public Lazy<T> get() {
        return DoubleCheck.lazy(provider);
    }

    /**
     * Creates a new {@link Provider Provider<Lazy<T>>} that decorates the given
     * {@link Provider}.
     *
     * @see #get()
     */
    public static <T> Provider<Lazy<T>> create(Provider<T> provider) {
        return new ProviderOfLazy<T>(checkNotNull(provider));
    }
}