| /* |
| * Copyright 2016 Google Inc. All Rights Reserved. |
| * |
| * 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.google.turbine.binder.env; |
| |
| import static java.util.Objects.requireNonNull; |
| |
| import com.google.turbine.binder.sym.Symbol; |
| import javax.annotation.Nullable; |
| |
| /** An {@link Env} that chains two existing envs together. */ |
| public class CompoundEnv<S extends Symbol, V> implements Env<S, V> { |
| |
| private final Env<S, ? extends V> base; |
| private final Env<S, ? extends V> env; |
| |
| private CompoundEnv(@Nullable Env<S, ? extends V> base, Env<S, ? extends V> env) { |
| this.base = base; |
| this.env = requireNonNull(env); |
| } |
| |
| @Override |
| public V get(S sym) { |
| V result = env.get(sym); |
| if (result != null) { |
| return result; |
| } |
| return base != null ? base.get(sym) : null; |
| } |
| |
| /** A chainable compound env with a single entry. */ |
| public static <S extends Symbol, V> CompoundEnv<S, V> of(Env<S, ? extends V> env) { |
| return new CompoundEnv<>(null, env); |
| } |
| |
| /** Adds an env to the chain. */ |
| public CompoundEnv<S, V> append(Env<S, ? extends V> env) { |
| return new CompoundEnv<>(this, env); |
| } |
| } |