visitExpression<R, C>  method 
Implementation
@override
R visitExpression<R, C>(o.ExpressionVisitor<R, C> visitor, C context) {
  return node._visibility == NodeReferenceVisibility.classPublic
      ? o.ReadClassMemberExpr(name!, type).visitExpression(visitor, context)
      : visitor.visitReadVarExpr(this, context);
}