/// <summary>
/// Returns the first element in a sequence that satisfies a specified condition.
/// </summary>
/// <typeparam name="T">The type of the elements of source.</typeparam>
/// <param name="seq">A collection to return an element from.</param>
/// <param name="filter">A function to test each element for a condition.</param>
/// <param name="token">The token that can be used to cancel enumeration.</param>
/// <returns>The first element in the sequence that matches to the specified filter; or empty value.</returns>
/// <exception cref="OperationCanceledException">The operation has been canceled.</exception>
public static ValueTask <Optional <T> > FirstOrEmptyAsync <T>(IAsyncEnumerable <T> seq, ValueFunc <T, bool> filter, CancellationToken token = default)
where T : notnull
=> NewSequence.FirstOrEmptyAsync(seq, filter, token);
/// <summary>
/// Obtains first value in the sequence; or <see cref="Optional{T}.None"/>
/// if sequence is empty.
/// </summary>
/// <typeparam name="T">Type of elements in the sequence.</typeparam>
/// <param name="seq">A sequence to check. Cannot be <see langword="null"/>.</param>
/// <param name="token">The token that can be used to cancel enumeration.</param>
/// <returns>The first element in the sequence; or <see cref="Optional{T}.None"/> if sequence is empty. </returns>
/// <exception cref="OperationCanceledException">The operation has been canceled.</exception>
public static ValueTask <Optional <T> > FirstOrEmptyAsync <T>(IAsyncEnumerable <T> seq, CancellationToken token = default)
=> NewSequence.FirstOrEmptyAsync(seq, token);