    001// Licensed under the Apache License, Version 2.0 (the "License");
    002// you may not use this file except in compliance with the License.
    003// You may obtain a copy of the License at
    004//
    005// http://www.apache.org/licenses/LICENSE-2.0
    006//
    007// Unless required by applicable law or agreed to in writing, software
    008// distributed under the License is distributed on an "AS IS" BASIS,
    009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    010// See the License for the specific language governing permissions and
    011// limitations under the License.
    012
    013package org.apache.tapestry5.func;
    014
    015import java.util.Collection;
    016import java.util.Comparator;
    017import java.util.List;
    018import java.util.Set;
    019
    020/**
    021 * @param T
    022 *         the type of data in the flow
    023 * @param FT
    024 *         the type of flow (either {@code Flow<T>} or {@code ZippedFlow<Tuple<T, ?>})
    025 * @since 5.3
    026 */
    027public interface FlowOperations<T, FT> extends Iterable<T>
    028{
    029    /**
    030     * Filters values, keeping only values where the predicate is true, returning a new Flow with
    031     * just the retained values.
    032     */
    033    FT filter(Predicate<? super T> predicate);
    034
    035    /**
    036     * Removes values where the predicate returns true, returning a new Flow with just the remaining
    037     * values.
    038     */
    039    FT remove(Predicate<? super T> predicate);
    040
    041    /**
    042     * Applies the worker to each element in the Flow, then returns the flow for further behaviors.
    043     *
    044     * Each is a non-lazy operation; it will fully realize the values of the Flow.
    045     */
    046    FT each(Worker<? super T> worker);
    047
    048    /**
    049     * Converts the Flow into an unmodifiable list of values. This is a non-lazy operation that will
    050     * fully realize the values of the Flow.
    051     */
    052    List<T> toList();
    053
    054    /**
    055     * Converts the Flow into an unmodifiable set of values. This is a non-lazy operation that will
    056     * fully realize the values of the Flow.
    057     */
    058    Set<T> toSet();
    059
    060    /**
    061     * Returns a new flow with the same elements but in reverse order.
    062     */
    063    FT reverse();
    064
    065    /**
    066     * Returns true if the Flow contains no values. This <em>may</em> realize the first value in the
    067     * Flow.
    068     */
    069    boolean isEmpty();
    070
    071    /**
    072     * Returns the first element in the Flow. Returns null for empty flows, but remember that null
    073     * is a valid element within a flow, so use {@link #isEmpty()} to determine if a flow is actually
    074     * empty. The first element can be realized without realizing the full Flow.
    075     */
    076    T first();
    077
    078    /**
    079     * Returns a new Flow containing all but the first element in this flow. If this flow has only a
    080     * single element, or is empty, this will return an empty Flow.
    081     */
    082    FT rest();
    083
    084    /**
    085     * Returns the number of values in this flow. This forces the realization of much of the flow
    086     * (i.e., because each value will need to be passed through any {@link Predicate}s).
    087     */
    088    int count();
    089
    090    /**
    091     * Sorts this flow using the comparator, forming a new flow. This is a non-lazy operation; it
    092     * will fully realize the elements of the Flow.
    093     */
    094    FT sort(Comparator<T> comparator);
    095
    096    /**
    097     * Returns a new flow containing just the first elements from this Flow.
    098     *
    099     * @param length
    100     *         maximum number of values in the Flow
    101     */
    102    FT take(int length);
    103
    104    /**
    105     * Returns a new flow with the first elements omitted.
    106     *
    107     * @param length
    108     *         number of values to drop
    109     */
    110    FT drop(int length);
    111
    112    /**
    113     * Returns a new Flow with the elements in the collection appended to this Flow. This is a lazy
    114     * operation.
    115     *
    116     * Note that the type of this method changed from {@code List} to {@link Collection} in Tapestry 5.4. This
    117     * is considered a compatible change.
    118     *
    119     * @param collection
    120     *         collection of elements to be appended
    121     */
    122    FT concat(Collection<? extends T> collection);
    123
    124    /**
    125     * Applies a Reducer to the values of the Flow. The Reducer is passed the initial value
    126     * and the first element from the Flow. The result is captured as the accumulator and passed
    127     * to the Reducer with the next value from the Flow, and so on. The final accumulator
    128     * value is returned. If the flow is empty, the initial value is returned.
    129     *
    130     * Reducing is a non-lazy operation; it will fully realize the values of the Flow.
    131     */
    132    <A> A reduce(Reducer<A, T> reducer, A initial);
    133
    134    /**
    135     * Removes null elements from the flow (null tuples from a ZippedFlow), leaving just the
    136     * non-null elements. This is a lazy operation.
    137     *
    138     * @since 5.3
    139     */
    140    FT removeNulls();
    141}