anchor.diff:  }
   
   class D {
  -  IOSink init(filename) {
  +  IOSink init(String filename) {
       IOSink _sinkF = new File(filename).openWrite(); // OK
       return _sinkF;
     }
  
positive.code: 
  class B1 {
    Socket _socketB1;
    Future init(filename) async {
      _socketB1 = await Socket.connect(null /*address*/, 1234); // OK
    }
  
    void dispose(filename) {
      _socketB1.destroy();
    }
  }
  
negative.code: // 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.
  
  // ignore_for_file: prefer_initializing_formals
  // ignore_for_file: unnecessary_new
  // ignore_for_file: unnecessary_this
  // ignore_for_file: unused_field
  // ignore_for_file: unused_local_variable
  // ignore_for_file: use_setters_to_change_properties
  
  import 'dart:async';
  import 'dart:io';
  
  class MockIOSink implements Sink {
    @override
  