Named tuple on delegate return type [Answered]

public delegate Task<Tuple<TEntity, bool>> AddUpdateCallbackDelegate(TEntity entity, IEnumerable<TEntity> dataSource);
public AddUpdateCallbackDelegate OnAddCallback { get; set; }

...
public async Task Test()
{
    var res = await OnAddCallback(...);
    res.Item1...
    res.Item2...
}

public delegate Task<Tuple<TEntity, bool>> AddUpdateCallbackDelegate(TEntity entity, IEnumerable<TEntity> dataSource);
public AddUpdateCallbackDelegate OnAddCallback { get; set; }

...
public async Task Test()
{
    var res = await OnAddCallback(...);
    res.Item1...
    res.Item2...
}