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