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stack_trace/lib/src/lazy_trace.dart

-// Copyright (c) 2013, 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 lazy_trace;
-
-import 'frame.dart';
-import 'trace.dart';
-
-/// A thunk for lazily constructing a [Trace].
-typedef Trace TraceThunk();
-
-/// A wrapper around a [TraceThunk]. This works around issue 9579 by avoiding
-/// the conversion of native [StackTrace]s to strings until it's absolutely
-/// necessary.
-class LazyTrace implements Trace {
-  final TraceThunk _thunk;
-  Trace _inner;
-
-  LazyTrace(this._thunk);
-
-  Trace get _trace {
-    if (_inner == null) _inner = _thunk();
-    return _inner;
-  }
-
-  List<Frame> get frames => _trace.frames;
-  StackTrace get vmTrace => _trace.vmTrace;
-  Trace get terse => new LazyTrace(() => _trace.terse);
-  Trace foldFrames(bool predicate(Frame frame), {bool terse: false}) =>
-    new LazyTrace(() => _trace.foldFrames(predicate, terse: terse));
-  String toString() => _trace.toString();
-
-  // Work around issue 14075.
-  set frames(_) => throw new UnimplementedError();
-}