struct Foo{
   int age;
   std::string name;
}

QVariant FooListModel::data(const QModelIndex &index, int role) const
{
    if (index.row() < 0 || index.row() > fooList.count())
        return QVariant();
    const Foo & foo = contacts[fooList.row()];
    if (role == AgeRole)       //AgeRole = 0
        return foo.age();
    else if (role == NameRole) //NameRole = 1
        return QString::fromStdString(foo.name());
    return QVariant();
}

struct Foo{
   int age;
   QString name;
}