private static FixedSingleResultOpt <TSource> WhereSingleImmediate <TSource>(this IEnumerable <TSource> source)
{
const bool usingPredicate = false;
if (source is IOpt <TSource> sourceOpt)
{
return(SingleResultOpt.GetFixedFromOpt(sourceOpt.ToFixed(), usingPredicate));
}
else if (source is IList <TSource> sourceList)
{
if (sourceList.Count > 1)
{
return(SingleResultOpt.GetFixedMoreThanOne <TSource>(usingPredicate));
}
else if (sourceList.Count == 0)
{
return(SingleResultOpt.GetFixedZero <TSource>(usingPredicate));
}
else
{
return(SingleResultOpt.GetFixedOne(usingPredicate, sourceList[0]));
}
}
else
{
using (var sourceEnumerator = source.GetEnumerator())
{
return(EnumeratorSingleToFixedOpt(sourceEnumerator, usingPredicate));
}
}
}
private static FixedSingleResultOpt <TSource> EnumeratorSingleToFixedOpt <TSource>(IEnumerator <TSource> source, bool usingPredicate)
{
if (source.MoveNext())
{
TSource value = source.Current;
if (source.MoveNext())
{
// More than one element
return(SingleResultOpt.GetFixedMoreThanOne <TSource>(usingPredicate));
}
else
{
// Exactly one element
return(SingleResultOpt.GetFixedOne(usingPredicate, value));
}
}
else
{
// No elements
return(SingleResultOpt.GetFixedZero <TSource>(usingPredicate));
}
}