126 lines
3.8 KiB
Java
126 lines
3.8 KiB
Java
/* Copyright 2017 Andrew Dawson
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*
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* This file is a part of Tusky.
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*
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* This program is free software; you can redistribute it and/or modify it under the terms of the
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* GNU General Public License as published by the Free Software Foundation; either version 3 of the
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* License, or (at your option) any later version.
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*
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* Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
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* the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
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* Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along with Tusky; if not,
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* see <http://www.gnu.org/licenses>. */
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package com.keylesspalace.tusky.util;
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import androidx.annotation.NonNull;
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import androidx.annotation.Nullable;
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/**
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* Created by charlag on 05/11/17.
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*
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* Class to represent sum type/tagged union/variant/ADT e.t.c.
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* It is either Left or Right.
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*/
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public final class Either<L, R> {
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/**
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* Constructs Left instance of either
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* @param left Object to be considered Left
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* @param <L> Left type
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* @param <R> Right type
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* @return new instance of Either which contains left.
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*/
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public static <L, R> Either<L, R> left(L left) {
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return new Either<>(left, false);
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}
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/**
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* Constructs Right instance of either
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* @param right Object to be considered Right
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* @param <L> Left type
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* @param <R> Right type
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* @return new instance of Either which contains right.
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*/
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public static <L, R> Either<L, R> right(R right) {
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return new Either<>(right, true);
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}
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private final Object value;
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// we need it because of the types erasure
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private boolean isRight;
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private Either(Object value, boolean isRight) {
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this.value = value;
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this.isRight = isRight;
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}
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public boolean isRight() {
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return isRight;
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}
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/**
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* Try to get contained object as a Left or throw an exception.
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* @throws AssertionError If contained value is Right
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* @return contained value as Right
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*/
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public @NonNull L getAsLeft() {
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if (isRight) {
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throw new AssertionError("Tried to get the Either as Left while it is Right");
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}
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//noinspection unchecked
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return (L) value;
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}
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/**
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* Try to get contained object as a Right or throw an exception.
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* @throws AssertionError If contained value is Left
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* @return contained value as Right
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*/
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public @NonNull R getAsRight() {
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if (!isRight) {
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throw new AssertionError("Tried to get the Either as Right while it is Left");
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}
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//noinspection unchecked
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return (R) value;
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}
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/**
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* Same as {@link #getAsLeft()} but returns {@code null} is the value if Right instead of
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* throwing an exception.
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* @return contained value as Left or null
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*/
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public @Nullable L getAsLeftOrNull() {
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if (isRight) {
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return null;
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}
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//noinspection unchecked
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return (L) value;
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}
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/**
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* Same as {@link #getAsRight()} but returns {@code null} is the value if Left instead of
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* throwing an exception.
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* @return contained value as Right or null
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*/
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public @Nullable R getAsRightOrNull() {
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if (!isRight) {
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return null;
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}
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//noinspection unchecked
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return (R) value;
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}
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@Override
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public boolean equals(Object obj) {
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if (this == obj) return true;
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if (obj == null) return false;
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if (!(obj instanceof Either)) return false;
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Either that = (Either) obj;
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return this.isRight == that.isRight &&
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(this.value == that.value ||
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this.value != null && this.value.equals(that.value));
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}
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}
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