public static ValueTask <TSource> SingleOrDefaultAsync <TSource>(this IAsyncEnumerable <TSource> source, CancellationToken cancellationToken = default)
{
if (source == null)
{
throw Error.ArgumentNull(nameof(source));
}
return(Core(source, cancellationToken));
async ValueTask <TSource> Core(IAsyncEnumerable <TSource> _source, CancellationToken _cancellationToken)
{
if (_source is IList <TSource> list)
{
switch (list.Count)
{
case 0: return(default);
case 1: return(list[0]);
}
throw Error.MoreThanOneElement();
}
await using (var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false))
{
if (!await e.MoveNextAsync())
{
return(default);
static async ValueTask <TSource> Core(IAsyncEnumerable <TSource> source, CancellationToken cancellationToken)
{
if (source is IList <TSource> list)
{
switch (list.Count)
{
case 0: throw Error.NoElements();
case 1: return(list[0]);
}
throw Error.MoreThanOneElement();
}
await using var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false);
if (!await e.MoveNextAsync())
{
throw Error.NoElements();
}
var result = e.Current;
if (await e.MoveNextAsync())
{
throw Error.MoreThanOneElement();
}
return(result);
}
public static TSource SingleOrDefault <TSource>(this IEnumerable <TSource> source)
{
if (source == null)
{
throw Error.ArgumentNull("source");
}
IList <TSource> list = source as IList <TSource>;
if (list != null)
{
switch (list.Count)
{
case 0: return(default(TSource));
case 1: return(list[0]);
}
}
else
{
using (IEnumerator <TSource> e = source.GetEnumerator())
{
if (!e.MoveNext())
{
return(default(TSource));
}
TSource result = e.Current;
if (!e.MoveNext())
{
return(result);
}
}
}
throw Error.MoreThanOneElement();
}
static async ValueTask <TSource> Core(IAsyncEnumerable <TSource> source, CancellationToken cancellationToken)
{
if (source is IList <TSource> list)
{
return(list.Count switch
{
0 => throw Error.NoElements(),
1 => list[0],
_ => throw Error.MoreThanOneElement(),
});
static async ValueTask <TSource> Core(IAsyncEnumerable <TSource> source, CancellationToken cancellationToken)
{
if (source is IList <TSource> list)
{
switch (list.Count)
{
case 0: return(default !);
case 1: return(list[0]);
}
throw Error.MoreThanOneElement();
}
await using (var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false))
{
if (!await e.MoveNextAsync())
{
return(default !);
