sdk/lib/_internal/js_runtime/lib/late_helper.dart

// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library _late_helper;

import 'dart:_internal' show LateError;

void throwLateFieldADI(String fieldName) => throw LateError.fieldADI(fieldName);

/// A boxed variable used for lowering uninitialized `late` variables when they
/// are locals or statics.
///
/// The [LateError]s produced have empty variable names.
// TODO(fishythefish): Support variable names depending on flags/compiler.
class _Cell {
  Object? _value;

  _Cell() {
    // `this` is a unique sentinel.
    _value = this;
  }

  @pragma('dart2js:tryInline')
  @pragma('dart2js:as:trust')
  T readLocal<T>() => _readLocal() as T;

  @pragma('dart2js:tryInline')
  @pragma('dart2js:as:trust')
  T readField<T>() => _readField() as T;

  Object? _readLocal() {
    if (identical(_value, this)) throw LateError.localNI('');
    return _value;
  }

  Object? _readField() {
    if (identical(_value, this)) throw LateError.fieldNI('');
    return _value;
  }

  void set value(Object? v) {
    _value = v;
  }

  void set finalLocalValue(Object? v) {
    if (!identical(_value, this)) throw LateError.localAI('');
    _value = v;
  }

  void set finalFieldValue(Object? v) {
    if (!identical(_value, this)) throw LateError.fieldAI('');
    _value = v;
  }
}

/// A boxed variable used for lowering `late` variables when they are
/// initialized locals.
///
/// The [LateError]s produced have empty variable names.
// TODO(fishythefish): Support variable names depending on flags/compiler.
class _InitializedCell {
  Object? _value;
  Object? Function() _initializer;

  _InitializedCell(this._initializer) {
    // `this` is a unique sentinel.
    _value = this;
  }

  @pragma('dart2js:tryInline')
  @pragma('dart2js:as:trust')
  T read<T>() => _read() as T;

  @pragma('dart2js:tryInline')
  @pragma('dart2js:as:trust')
  T readFinal<T>() => _readFinal() as T;

  Object? _read() {
    if (identical(_value, this)) _value = _initializer();
    return _value;
  }

  Object? _readFinal() {
    if (identical(_value, this)) {
      final result = _initializer();
      if (!identical(_value, this)) throw LateError.localADI('');
      _value = result;
    }
    return _value;
  }

  void set value(Object? v) {
    _value = v;
  }

  void set finalValue(Object? v) {
    if (!identical(_value, this)) throw LateError.localAI('');
    _value = v;
  }
}