public static TSource Single <TEnumerable, TEnumerator, TSource>(this TEnumerable source)
where TEnumerable : IReadOnlyCollection <TSource>
where TEnumerator : IEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
var count = source.Count;
if (count == 0)
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
if (count > 1)
{
ThrowHelper.ThrowNotSingleSequence <TSource>();
}
using (var enumerator = Dynamic.GetEnumerator <TEnumerable, TEnumerator, TSource> .Invoke(source))
{
enumerator.MoveNext();
return(enumerator.Current);
}
}
public static TSource Single <TEnumerable, TEnumerator, TSource>(this TEnumerable source, Func <TSource, bool> predicate)
where TEnumerable : IValueReadOnlyList <TSource, TEnumerator>
where TEnumerator : struct, IValueEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
var count = source.Count();
if (count == 0)
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
for (var index = 0; index < count; index++)
{
if (predicate(source[index]))
{
var first = source[index];
for (index++; index < count; index++)
{
if (predicate(source[index]))
{
ThrowHelper.ThrowNotSingleSequence <TSource>();
}
}
return(first);
}
}
return(ThrowHelper.ThrowEmptySequence <TSource>());
}
public static TSource Single <TEnumerable, TEnumerator, TSource>(this TEnumerable source, Func <TSource, bool> predicate)
where TEnumerable : IValueEnumerable <TSource, TEnumerator>
where TEnumerator : struct, IValueEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
using (var enumerator = source.GetValueEnumerator())
{
while (enumerator.TryMoveNext(out var first))
{
if (predicate(first))
{
// found first, keep going until end or find second
while (enumerator.TryMoveNext(out var current))
{
if (predicate(current))
{
ThrowHelper.ThrowNotSingleSequence <TSource>();
}
}
return(first);
}
}
return(ThrowHelper.ThrowEmptySequence <TSource>());
}
}
public static TSource Single <TEnumerable, TEnumerator, TSource>(this TEnumerable source)
where TEnumerable : IValueReadOnlyCollection <TSource, TEnumerator>
where TEnumerator : struct, IValueEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
var count = source.Count();
if (count == 0)
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
if (count > 1)
{
ThrowHelper.ThrowNotSingleSequence <TSource>();
}
using (var enumerator = source.GetValueEnumerator())
{
enumerator.TryMoveNext(out var current);
return(current);
}
}
public static TSource First <TEnumerable, TEnumerator, TSource>(this TEnumerable source, Func <TSource, bool> predicate)
where TEnumerable : IReadOnlyList <TSource>
where TEnumerator : IEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
var count = source.Count;
if (count == 0)
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
for (var index = 0; index < count; index++)
{
if (predicate(source[index]))
{
return(source[index]);
}
}
return(ThrowHelper.ThrowEmptySequence <TSource>());
}
public static TSource Single <TEnumerable, TEnumerator, TSource>(this TEnumerable source)
where TEnumerable : IEnumerable <TSource>
where TEnumerator : IEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
using (var enumerator = Dynamic.GetEnumerator <TEnumerable, TEnumerator, TSource> .Invoke(source))
{
if (!enumerator.MoveNext())
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
var first = enumerator.Current;
if (enumerator.MoveNext())
{
ThrowHelper.ThrowNotSingleSequence <TSource>();
}
return(first);
}
}
public static TSource Single <TEnumerable, TEnumerator, TSource>(this TEnumerable source, Func <TSource, bool> predicate)
where TEnumerable : IEnumerable <TSource>
where TEnumerator : IEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
using (var enumerator = Dynamic.GetEnumerator <TEnumerable, TEnumerator, TSource> .Invoke(source))
{
while (enumerator.MoveNext())
{
var first = enumerator.Current;
if (predicate(first))
{
// found first, keep going until end or find second
while (enumerator.MoveNext())
{
if (predicate(enumerator.Current))
{
ThrowHelper.ThrowNotSingleSequence <TSource>();
}
}
return(first);
}
}
return(ThrowHelper.ThrowEmptySequence <TSource>());
}
}
public static ref readonly TSource First <TSource>(this ReadOnlySpan <TSource> source)
{
if (source.Length == 0)
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
return(ref source[0]);
public static ref readonly TSource First <TSource>(this TSource[] source)
{
if (source is null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
if (source.Length == 0)
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
return(ref source[0]);
public static TSource First <TEnumerable, TEnumerator, TSource>(this TEnumerable source)
where TEnumerable : IValueReadOnlyList <TSource, TEnumerator>
where TEnumerator : struct, IValueEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
if (source.Count() == 0)
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
return(source[0]);
}
public static TSource First <TEnumerable, TEnumerator, TSource>(this TEnumerable source)
where TEnumerable : IValueEnumerable <TSource, TEnumerator>
where TEnumerator : struct, IValueEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
using (var enumerator = source.GetValueEnumerator())
{
if (enumerator.TryMoveNext(out var current))
{
return(current);
}
ThrowHelper.ThrowEmptySequence <TSource>();
return(default);
public static TSource Single <TEnumerable, TEnumerator, TSource>(this TEnumerable source)
where TEnumerable : IReadOnlyList <TSource>
where TEnumerator : IEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
var count = source.Count;
if (count == 0)
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
if (count > 1)
{
ThrowHelper.ThrowNotSingleSequence <TSource>();
}
return(source[0]);
}
public static TSource First <TEnumerable, TEnumerator, TSource>(this TEnumerable source, Func <TSource, bool> predicate)
where TEnumerable : IEnumerable <TSource>
where TEnumerator : IEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
using (var enumerator = Dynamic.GetEnumerator <TEnumerable, TEnumerator, TSource> .Invoke(source))
{
while (enumerator.MoveNext())
{
var current = enumerator.Current;
if (predicate(current))
{
return(current);
}
}
return(ThrowHelper.ThrowEmptySequence <TSource>());
}
}
public static TSource Single <TEnumerable, TEnumerator, TSource>(this TEnumerable source)
where TEnumerable : IValueEnumerable <TSource, TEnumerator>
where TEnumerator : struct, IValueEnumerator <TSource>
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(nameof(source));
}
using (var enumerator = source.GetValueEnumerator())
{
if (!enumerator.TryMoveNext(out var first))
{
ThrowHelper.ThrowEmptySequence <TSource>();
}
if (enumerator.TryMoveNext())
{
ThrowHelper.ThrowNotSingleSequence <TSource>();
}
return(first);
}
}