Method TagFirstLast

TagFirstLast<TSource>(IAsyncEnumerable<TSource>)

Returns a sequence resulting from applying a function to each element in the source sequence with additional parameters indicating whether the element is the first and/or last of the sequence.

Declaration
public static IAsyncEnumerable<(TSource item, bool isFirst, bool isLast)> TagFirstLast<TSource>(this IAsyncEnumerable<TSource> source)
Parameters
Type Name Description
IAsyncEnumerable<TSource> source

The source sequence.
Returns
Type Description
IAsyncEnumerable<(TSource item, bool isFirst, bool isLast)>

Returns the resulting sequence.
Type Parameters
Name Description
TSource

The type of the elements of source.
Remarks

This operator uses deferred execution and streams its results.

Examples
var numbers = new[] { 123, 456, 789 };
var result = numbers.TagFirstLast();

The result variable, when iterated over, will yield (item: 123, isFirst: True, isLast: False), (item: 456, isFirst: False, isLast: False) and (item: 789, isFirst: False, isLast: True) in turn.

Exceptions
Type Condition
ArgumentNullException

source is null.

TagFirstLast<TSource, TResult>(IAsyncEnumerable<TSource>, Func<TSource, bool, bool, TResult>)

Returns a sequence resulting from applying a function to each element in the source sequence with additional parameters indicating whether the element is the first and/or last of the sequence.

Declaration
public static IAsyncEnumerable<TResult> TagFirstLast<TSource, TResult>(this IAsyncEnumerable<TSource> source, Func<TSource, bool, bool, TResult> resultSelector)
Parameters
Type Name Description
IAsyncEnumerable<TSource> source

The source sequence.
Func<TSource, bool, bool, TResult> resultSelector

A function that determines how to project the each element along with its first or last tag.
Returns
Type Description
IAsyncEnumerable<TResult>

Returns the resulting sequence.
Type Parameters
Name Description
TSource

The type of the elements of source.
TResult

The type of the element of the returned sequence.
Remarks

This operator uses deferred execution and streams its results.

Examples
var numbers = new[] { 123, 456, 789 };
var result = numbers.TagFirstLast((num, fst, lst) => new
             {
                 Number = num,
                 IsFirst = fst, IsLast = lst
             });

The result variable, when iterated over, will yield { Number = 123, IsFirst = True, IsLast = False }, { Number = 456, IsFirst = False, IsLast = False } and { Number = 789, IsFirst = False, IsLast = True } in turn.

Exceptions
Type Condition
ArgumentNullException

source or resultSelector is null.