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Count.cs
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Count.cs
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Collections;
using System.Collections.Generic;
namespace System.Linq
{
public static partial class Enumerable
{
public static int Count<TSource>(this IEnumerable<TSource> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
if (source is ICollection<TSource> collectionoft)
{
return collectionoft.Count;
}
if (source is IIListProvider<TSource> listProv)
{
return listProv.GetCount(onlyIfCheap: false);
}
if (source is ICollection collection)
{
return collection.Count;
}
int count = 0;
using (IEnumerator<TSource> e = source.GetEnumerator())
{
checked
{
while (e.MoveNext())
{
count++;
}
}
}
return count;
}
public static int Count<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
if (predicate == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.predicate);
}
int count = 0;
foreach (TSource element in source)
{
checked
{
if (predicate(element))
{
count++;
}
}
}
return count;
}
/// <summary>
/// Attempts to determine the number of elements in a sequence without forcing an enumeration.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source" />.</typeparam>
/// <param name="source">A sequence that contains elements to be counted.</param>
/// <param name="count">
/// When this method returns, contains the count of <paramref name="source" /> if successful,
/// or zero if the method failed to determine the count.</param>
/// <returns>
/// <see langword="true" /> if the count of <paramref name="source"/> can be determined without enumeration;
/// otherwise, <see langword="false" />.
/// </returns>
/// <remarks>
/// The method performs a series of type tests, identifying common subtypes whose
/// count can be determined without enumerating; this includes <see cref="ICollection{T}"/>,
/// <see cref="ICollection"/> as well as internal types used in the LINQ implementation.
///
/// The method is typically a constant-time operation, but ultimately this depends on the complexity
/// characteristics of the underlying collection implementation.
/// </remarks>
public static bool TryGetNonEnumeratedCount<TSource>(this IEnumerable<TSource> source, out int count)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
if (source is ICollection<TSource> collectionoft)
{
count = collectionoft.Count;
return true;
}
if (source is IIListProvider<TSource> listProv)
{
int c = listProv.GetCount(onlyIfCheap: true);
if (c >= 0)
{
count = c;
return true;
}
}
if (source is ICollection collection)
{
count = collection.Count;
return true;
}
count = 0;
return false;
}
public static long LongCount<TSource>(this IEnumerable<TSource> source)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
long count = 0;
using (IEnumerator<TSource> e = source.GetEnumerator())
{
checked
{
while (e.MoveNext())
{
count++;
}
}
}
return count;
}
public static long LongCount<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
if (source == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
}
if (predicate == null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.predicate);
}
long count = 0;
foreach (TSource element in source)
{
checked
{
if (predicate(element))
{
count++;
}
}
}
return count;
}
}
}