Suggests replacing expressions with equivalent expressions that are more readable, or use modern language features, or improve performance. The analyzer doesn't make any suggestions if the current language version doesn't support the replacement.

• TSource ElementAt<TSource>(this IEnumerable<TSource> source, int index)
• TSource ElementAt<TSource>(this IEnumerable<TSource> source, Index index)

If source is an indexable** collection or a string:

Case	Suggested replacement	When suggested
source.ElementAt(index)	source[index]	always

If source is a distinct*** collection:

Case	Warns
source.ElementAt(index)	that items should not be accessed by an index

• TSource? ElementAtOrDefault<TSource>(this IEnumerable<TSource> source, int index)
• TSource? ElementAtOrDefault<TSource>(this IEnumerable<TSource> source, Index index)

If source is a distinct*** collection:

Case	Warns
source.ElementAt(index)	that items should not be accessed by an index

• TSource First<TSource>(this IEnumerable<TSource> source)

If source is an indexable** collection or a string:

Case	Suggested replacement	When suggested
source.First()	source[0]	always

If source is a distinct*** collection:

Case	Warns
source.First()	that items should not be accessed by an index

• TSource? FirstOrDefault<TSource>(this IEnumerable<TSource> source)
• TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, TSource defaultValue)

If source is an indexable** collection or a string:

Case	Suggested replacement	When suggested
source.FirstOrDefault()	source is [var first, ..] ? first : default	source is not null here
source.FirstOrDefault(defaultValue)	source is [var first, ..] ? first : defaultValue	source is not null here

If source is a distinct*** collection:

Case	Warns
source.FirstOrDefault()	that items should not be accessed by an index
source.FirstOrDefault(defaultValue)	that items should not be accessed by an index

• TSource Last<TSource>(this IEnumerable<TSource> source)

If source is an indexable** collection or a string:

Case	Suggested replacement	When suggested
source.Last()	source[^1]	always

If source is a distinct*** collection:

Case	Warns
source.Last()	that items should not be accessed by an index

• TSource? LastOrDefault<TSource>(this IEnumerable<TSource> source)
• TSource LastOrDefault<TSource>(this IEnumerable<TSource> source, TSource defaultValue)

If source is an indexable** collection or a string:

Case	Suggested replacement	When suggested
source.LastOrDefault()	source is [.., var last] ? last : default	source is not null here
source.LastOrDefault(defaultValue)	source is [.., var last] ? last : defaultValue	source is not null here

If source is a distinct*** collection:

Case	Warns
source.LastOrDefault()	that items should not be accessed by an index
source.LastOrDefault(defaultValue)	that items should not be accessed by an index

• long LongCount<TSource>(this IEnumerable<TSource> source)

Case	Suggested replacement	When suggested
source.LongCount()	source.Length	source is a string or an array
source.LongCount()	source.Count	source is a collection*

• TSource Single<TSource>(this IEnumerable<TSource> source)

If source is an indexable** collection or a string:

Case	Suggested replacement	When suggested
source.Single()	source is [var item] ? item : throw new InvalidOperationException("... either empty or contains more than one element")	source is not null here

• TSource? SingleOrDefault<TSource>(this IEnumerable<TSource> source)
• TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source, TSource defaultValue)

If source is an indexable** collection or a string:

Case	Suggested replacement	When suggested
source.SingleOrDefault()	source switch { [] => default, [var item] => item, _ => throw new InvalidOperationException("... contains more than one element") }	source is not null here

* Collections, which implement Collection<T> or IReadOnlyCollection<T> (including single-dimensional arrays), or strings.

**Indexable collections are collections, which implement IList<T> (including single-dimensional arrays) or IReadOnlyList<T>.

***Distinct collections are non-indexable collections, which implement ISet<T> or IReadOnlySet<T>, or the Dictionary<K,V>.KeyCollection.

💡 Quick-fixes are available.

• list patterns might introduce variable with conflicting names

💡 The analyzers can be deactivated in the ReSharper Options dialog.

• CA1826: Use property instead of Linq Enumerable method