// Copyright 2019 The Bazel Authors. 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.devtools.build.lib.syntax;

import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
import com.google.devtools.build.lib.skylarkinterface.SkylarkModule;
import com.google.devtools.build.lib.skylarkinterface.SkylarkPrinter;
import com.google.devtools.build.lib.skylarkinterface.SkylarkValue;

/** The type of the Starlark None value. */
@SkylarkModule(name = "NoneType", documented = false, doc = "The type of the Starlark None value.")
@Immutable
public final class NoneType implements SkylarkValue {

  static final NoneType NONE = new NoneType();

  private NoneType() {}

  @Override
  public String toString() {
    return "None";
  }

  @Override
  public boolean isImmutable() {
    return true;
  }

  @Override
  public boolean truth() {
    return false;
  }

  @Override
  public void repr(SkylarkPrinter printer) {
    printer.append("None");
  }
}