/// <summary>
/// create <see cref="HashSet{T}"/> from <see cref="IEnumerable{T}"/>
/// with specified <see cref="IEqualityComparer{T}"/>
/// </summary>
public static HashSet <T> ToHashSet <T>(this IEnumerable <T> source, IEqualityComparer <T> comparer)
{
source.ThrowIfArgumentNull(nameof(source));
comparer.ThrowIfArgumentNull(nameof(comparer));
return(new HashSet <T>(source, comparer));
}
/// <summary>
/// Returns true if <paramref name="value"/> is in <paramref name="source"/>
/// by using a specified <paramref name="comparer"/>.
/// </summary>
public static bool In <T>(this T value, IEnumerable <T> source, IEqualityComparer <T> comparer)
{
source.ThrowIfArgumentNull(nameof(source));
comparer.ThrowIfArgumentNull(nameof(comparer));
return(source.Contains(value, comparer));
}