/// <summary>
/// Applies the given function to each element of the sequence and returns the list comprised of the results
/// for each element where the function returns non-empty value.
/// </summary>
/// <param name="source">The input sequence.</param>
/// <param name="chooser">A function to transform items.</param>
/// <returns>The result sequence.</returns>
/// <exception cref="T:System.ArgumentNullException">
/// Thrown if <paramref name="source" /> or <paramref name="chooser" /> is <c>null</c>.
/// </exception>
public static IEnumerable <TResult> MaybeChoose <TSource, TResult>(this IEnumerable <TSource> source, Func <TSource, Maybe <TResult> > chooser)
{
RuntimeAssert.ArgumentNotNull(source, nameof(source));
RuntimeAssert.ArgumentNotNull(chooser, nameof(chooser));
foreach (var item in source)
{
if (chooser(item).TryGetValue(out var result))
{
yield return(result);
}
}
}
/// <summary>
/// Creates new object comparer. Both order and eqaulity comparison are performed using
/// <paramref name="comparer" /> and hash code generated using <paramref name="getHashCode" />.
/// </summary>
/// <param name="comparer">Source comparer.</param>
/// <param name="getHashCode">Source get hash code function.</param>
/// <returns>Newly created object comparer.</returns>
public static ObjectComparer <T> Create(IComparer <T> comparer, Func <T, int> getHashCode)
{
RuntimeAssert.ArgumentNotNull(comparer, nameof(comparer));
RuntimeAssert.ArgumentNotNull(getHashCode, nameof(getHashCode));
return(new ExplicitObjectComparer(comparer, getHashCode));
}
/// <summary>
/// Returns the first element of a sequence that setisfies specified predicate if any or empty container.
/// </summary>
/// <param name="source">Source sequence.</param>
/// <param name="predicate">Predicate to apply.</param>
/// <returns>
/// Either empty <see cref="T:NCoreUtils.Maybe{TResult}" /> or
/// <see cref="T:NCoreUtils.Maybe{TResult}" /> containing the first element.
/// </returns>
public static Maybe <T> MaybeFirst <T>(this IEnumerable <T> source, Func <T, bool> predicate)
{
RuntimeAssert.ArgumentNotNull(source, nameof(source));
return(source.Where(predicate).Select(Maybe.AsMaybe).FirstOrDefault());
}