anchor.diff:          Expression extends Object, Variable extends Object, Type extends Object>
       implements FlowAnalysis<Node, Statement, Expression, Variable, Type> {
     /// The [TypeOperations], used to access types, and check subtyping.
  +  @override
     final TypeOperations<Variable, Type> typeOperations;
   
     /// Stack of [_FlowContext] objects representing the statements and
  
positive.code:   /// Return `true` if the current state is reachable.
    bool get isReachable;
  
    /// Call this method after visiting an "as" expression.
    ///
    /// [subExpression] should be the expression to which the "as" check was
  
negative.code:   @override
    bool get isReachable =>
        _wrap('isReachable', () => _wrapped.isReachable, isQuery: true);
  
    @override
    TypeOperations<Variable, Type> get typeOperations => _wrapped.typeOperations;
  
    @override
    void asExpression_end(Expression subExpression, Type type) {
  