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IAsyncEnumerableExtensions.cs
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IAsyncEnumerableExtensions.cs
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using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
namespace System.Collections.Async
{
/// <summary>
/// Extension methods for <see cref="IAsyncEnumerable{T}"/> interface
/// </summary>
[ComponentModel.EditorBrowsable(ComponentModel.EditorBrowsableState.Never)]
public static class IAsyncEnumerableExtensions
{
#region First / FirstOrDefault
/// <summary>
/// Returns the first element in the <see cref="IAsyncEnumerable{T}"/>.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">An <see cref="IAsyncEnumerable{T}"/> to return an element from.</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static Task<TSource> FirstAsync<TSource>(
this IAsyncEnumerable<TSource> source,
CancellationToken token = default(CancellationToken))
{
return FirstAsync(source, _ => true, token);
}
/// <summary>
/// Returns the first element in a sequence that satisfies a specified condition.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">An <see cref="IAsyncEnumerable{T}"/> to return an element from.</param>
/// <param name="predicate">A function to test each element for a condition.</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static async Task<TSource> FirstAsync<TSource>(
this IAsyncEnumerable<TSource> source,
Func<TSource, bool> predicate,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (null == predicate)
throw new ArgumentNullException(nameof(predicate));
using (var enumerator = await source.GetAsyncEnumeratorAsync(token).ConfigureAwait(false))
while (await enumerator.MoveNextAsync(token).ConfigureAwait(false))
if (predicate(enumerator.Current))
return enumerator.Current;
throw new InvalidOperationException("No Matching Element Found");
}
/// <summary>
/// Returns the first element in the <see cref="IAsyncEnumerable{T}"/>, or a default value if no element is found.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">An <see cref="IAsyncEnumerable{T}"/> to return an element from.</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static Task<TSource> FirstOrDefaultAsync<TSource>(
this IAsyncEnumerable<TSource> source,
CancellationToken token = default(CancellationToken))
{
return FirstOrDefaultAsync(source, _ => true, token);
}
/// <summary>
/// Returns the first element in a sequence that satisfies a specified condition, or a default value if no element is found.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">An <see cref="IAsyncEnumerable{T}"/> to return an element from.</param>
/// <param name="predicate">A function to test each element for a condition.</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static async Task<TSource> FirstOrDefaultAsync<TSource>(
this IAsyncEnumerable<TSource> source,
Func<TSource, bool> predicate,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (null == predicate)
throw new ArgumentNullException(nameof(predicate));
using (var enumerator = await source.GetAsyncEnumeratorAsync(token).ConfigureAwait(false))
while (await enumerator.MoveNextAsync(token).ConfigureAwait(false))
if (predicate(enumerator.Current))
return enumerator.Current;
return default(TSource);
}
#endregion
#region Select
/// <summary>
/// Projects each element of a sequence into a new form.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <typeparam name="TResult">The type of the value returned by <paramref name="source"/>.</typeparam>
/// <param name="source">A sequence of values to invoke a transform function on.</param>
/// <param name="selector">A transform function to apply to each element.</param>
/// <param name="oneTimeUse">When <c>true</c> the enumeration can be performed once only and <see cref="AsyncEnumerator{T}.Reset"/> method is not allowed</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static IAsyncEnumerable<TResult> SelectAsync<TSource, TResult>(
this IAsyncEnumerable<TSource> source,
Func<TSource, TResult> selector,
bool oneTimeUse = false,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (null == selector)
throw new ArgumentNullException(nameof(selector));
return new AsyncEnumerable<TResult>(
yield =>
source.ForEachAsync(
item => yield.ReturnAsync(selector(item)),
token),
oneTimeUse);
}
/// <summary>
/// Projects each element of a sequence into a new form.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <typeparam name="TResult">The type of the value returned by <paramref name="source"/>.</typeparam>
/// <param name="source">A sequence of values to invoke a transform function on.</param>
/// <param name="selector">A transform function to apply to each source element; the second parameter of the function represents the index of the source element.</param>
/// <param name="oneTimeUse">When <c>true</c> the enumeration can be performed once only and <see cref="AsyncEnumerator{T}.Reset"/> method is not allowed</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static IAsyncEnumerable<TResult> SelectAsync<TSource, TResult>(
this IAsyncEnumerable<TSource> source,
Func<TSource, long, TResult> selector,
bool oneTimeUse = false,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (null == selector)
throw new ArgumentNullException(nameof(selector));
return new AsyncEnumerable<TResult>(
yield =>
source.ForEachAsync(
(item, index) => yield.ReturnAsync(selector(item, index)),
token),
oneTimeUse);
}
#endregion
#region Take / TakeWhile
/// <summary>
/// Returns a specified number of contiguous elements from the start of a sequence.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">A sequence to return elements from.</param>
/// <param name="count">The number of elements to return.</param>
/// <param name="oneTimeUse">When <c>true</c> the enumeration can be performed once only and <see cref="AsyncEnumerator{T}.Reset"/> method is not allowed</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static IAsyncEnumerable<TSource> TakeAsync<TSource>(
this IAsyncEnumerable<TSource> source,
int count,
bool oneTimeUse = false,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (count <= 0)
return AsyncEnumerable<TSource>.Empty;
return new AsyncEnumerable<TSource>(
async yield =>
{
using (var enumerator = await source.GetAsyncEnumeratorAsync(token).ConfigureAwait(false))
while (count > 0)
{
if (await enumerator.MoveNextAsync(token).ConfigureAwait(false))
await yield.ReturnAsync(enumerator.Current).ConfigureAwait(false);
count--;
}
},
oneTimeUse);
}
/// <summary>
/// Returns elements from a sequence as long as a specified condition is true.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">A sequence to return elements from.</param>
/// <param name="predicate">A function to test each element for a condition.</param>
/// <param name="oneTimeUse">When <c>true</c> the enumeration can be performed once only and <see cref="AsyncEnumerator{T}.Reset"/> method is not allowed</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static IAsyncEnumerable<TSource> TakeWhileAsync<TSource>(
this IAsyncEnumerable<TSource> source,
Func<TSource, bool> predicate,
bool oneTimeUse = false,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (null == predicate)
throw new ArgumentNullException(nameof(predicate));
return new AsyncEnumerable<TSource>(
async yield =>
{
using (var enumerator = await source.GetAsyncEnumeratorAsync(token).ConfigureAwait(false))
while (await enumerator.MoveNextAsync(token).ConfigureAwait(false))
if (predicate(enumerator.Current))
await yield.ReturnAsync(enumerator.Current).ConfigureAwait(false);
else
break;
},
oneTimeUse);
}
#endregion
#region ToList
/// <summary>
/// Creates a list of elements asynchronously from the enumerable source
/// </summary>
/// <typeparam name="T">The type of the elements of source</typeparam>
/// <param name="source">The collection of elements</param>
/// <param name="cancellationToken">A cancellation token to cancel the async operation</param>
public static async Task<List<T>> ToListAsync<T>(this IAsyncEnumerable<T> source, CancellationToken cancellationToken = default(CancellationToken))
{
var resultList = new List<T>();
using (var enumerator = await source.GetAsyncEnumeratorAsync(cancellationToken).ConfigureAwait(false))
{
while (await enumerator.MoveNextAsync(cancellationToken).ConfigureAwait(false))
{
resultList.Add(enumerator.Current);
}
}
return resultList;
}
#endregion
#region ToArray
/// <summary>
/// Creates an array of elements asynchronously from the enumerable source
/// </summary>
/// <typeparam name="T">The type of the elements of source</typeparam>
/// <param name="source">The collection of elements</param>
/// <param name="cancellationToken">A cancellation token to cancel the async operation</param>
public static async Task<T[]> ToArrayAsync<T>(this IAsyncEnumerable<T> source, CancellationToken cancellationToken = default(CancellationToken))
{
var list = await source.ToListAsync(cancellationToken).ConfigureAwait(false);
return list.ToArray();
}
#endregion
#region Skip / SkipWhile
/// <summary>
/// An <see cref="IAsyncEnumerable{T}"/> to return elements from.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">An <see cref="IAsyncEnumerable{T}"/> to return elements from.</param>
/// <param name="count">The number of elements to skip before returning the remaining elements.</param>
/// <param name="oneTimeUse">When <c>true</c> the enumeration can be performed once only and <see cref="AsyncEnumerator{T}.Reset"/> method is not allowed</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static IAsyncEnumerable<TSource> SkipAsync<TSource>(
this IAsyncEnumerable<TSource> source,
int count,
bool oneTimeUse = false,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
return new AsyncEnumerable<TSource>(
async yield =>
{
using (var enumerator = await source.GetAsyncEnumeratorAsync(token).ConfigureAwait(false))
while (await enumerator.MoveNextAsync(token).ConfigureAwait(false))
if (count-- <= 0)
await yield.ReturnAsync(enumerator.Current).ConfigureAwait(false);
},
oneTimeUse);
}
/// <summary>
/// Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">An <see cref="IAsyncEnumerable{T}"/> to return elements from.</param>
/// <param name="predicate">A function to test each element for a condition.</param>
/// <param name="oneTimeUse">When <c>true</c> the enumeration can be performed once only and <see cref="AsyncEnumerator{T}.Reset"/> method is not allowed</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static IAsyncEnumerable<TSource> SkipWhileAsync<TSource>(
this IAsyncEnumerable<TSource> source,
Func<TSource, bool> predicate,
bool oneTimeUse = false,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (null == predicate)
throw new ArgumentNullException(nameof(predicate));
return new AsyncEnumerable<TSource>(
async yield =>
{
var yielding = false;
using (var enumerator = await source.GetAsyncEnumeratorAsync(token).ConfigureAwait(false))
while (await enumerator.MoveNextAsync(token).ConfigureAwait(false))
{
if (!yielding && !predicate(enumerator.Current))
yielding = true;
if (yielding)
await yield.ReturnAsync(enumerator.Current).ConfigureAwait(false);
}
},
oneTimeUse);
}
#endregion
#region Where
/// <summary>
/// Filters a sequence of values based on a predicate.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">An <see cref="IAsyncEnumerable{T}"/> to filter.</param>
/// <param name="predicate">A function to test each element for a condition.</param>
/// <param name="oneTimeUse">When <c>true</c> the enumeration can be performed once only and <see cref="AsyncEnumerator{T}.Reset"/> method is not allowed</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static IAsyncEnumerable<TSource> WhereAsync<TSource>(
this IAsyncEnumerable<TSource> source,
Func<TSource, bool> predicate,
bool oneTimeUse = false,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (null == predicate)
throw new ArgumentNullException(nameof(predicate));
return new AsyncEnumerable<TSource>(
async yield =>
{
using (var enumerator = await source.GetAsyncEnumeratorAsync(token).ConfigureAwait(false))
while (await enumerator.MoveNextAsync(token).ConfigureAwait(false))
{
if (predicate(enumerator.Current))
await yield.ReturnAsync(enumerator.Current).ConfigureAwait(false);
}
},
oneTimeUse);
}
/// <summary>
/// Projects each element of a sequence into a new form.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/></typeparam>
/// <param name="source">An <see cref="IAsyncEnumerable{T}"/> to filter.</param>
/// <param name="predicate">A function to test each element for a condition; the second parameter of the function represents the index of the source element.</param>
/// <param name="oneTimeUse">When <c>true</c> the enumeration can be performed once only and <see cref="AsyncEnumerator{T}.Reset"/> method is not allowed</param>
/// <param name="token">A <see cref="CancellationToken"/> that can halt enumeration of <paramref name="source"/></param>
public static IAsyncEnumerable<TSource> WhereAsync<TSource>(
this IAsyncEnumerable<TSource> source,
Func<TSource, long, bool> predicate,
bool oneTimeUse = false,
CancellationToken token = default(CancellationToken))
{
if (null == source)
throw new ArgumentNullException(nameof(source));
if (null == predicate)
throw new ArgumentNullException(nameof(predicate));
long index = 0;
return new AsyncEnumerable<TSource>(
async yield =>
{
using (var enumerator = await source.GetAsyncEnumeratorAsync(token).ConfigureAwait(false))
while (await enumerator.MoveNextAsync(token).ConfigureAwait(false))
{
if (predicate(enumerator.Current, index))
await yield.ReturnAsync(enumerator.Current).ConfigureAwait(false);
index++;
}
},
oneTimeUse);
}
#endregion
}
}