Summary

Add IsEmpty method.

• Judges that IEnumerable<T> is empty.
• IEnumerable<T> extension method. New LINQ to Objects member.
• Someone uses “Count() == 0” incorrectly. IsEmpty method helps them.

API

public static class Enumerable
{
    public static bool IsEmpty<TSource>(this IEnumerable<TSource> source);
}

Discussion [UPADTED]

How about use !enumrable.Any()?

I think enumerable.IsEmpty() is better than !enumerable.Any() with next reasons.

• IsEmpty() is more clear and more explicit to check that enumerable is empty than !enumerable.Any().
• For C# beginner, !enumerable.Any() to check empty is not familiar, not clear and not easy to find.

I think everyone who participates in this issue is familiar to C# and LINQ. So we know how to use !enumerable.Any() and reason to use !enumerable.Any().

But I think that C# beginner is not same. Please imagine C# beginner. It is a little difficult to find usage of !enumerable.Any() to check empty for them. I think IsEmpty is so easy to find and useful to them.

Background

There are no method or property to judge that Array, IEnumerable<T> and List<T> etc are empty or not.

Someone uses “Count() == 0” incorrectly to judge that IEnumerable<T> is empty or not. This is bad usage. Next code is an example.

Next code read all line twice. To judge target.txt is empty, we do not need read all lines. If target.txt is huge, it is so bad.

IEnumerable<string> lines = File.ReadLines("target.txt");
// Bad solution
if(lines.Count() == 0) {
    Console.WriteLine("target.txt is empty.");
    return ;
}

// iterate all line and use it.

Good practice is to use Any method and ! to judge is empty. This can judge that file is empty or not without reading all lines.

IEnumerable<string> lines = File.ReadLines("target.txt");
// Current good solution
if(!lines.Any()) {
    Console.WriteLine("target.txt is empty.");
    return ;
}

// iterate all line and use it.

By the way, I do NOT think this is BEST way.

Solution and Usage

I suggest IsEmpty method to IEnumerable<T> as extension method. IsEmpty judeges that Array, IEnumerable<T> and List<T> etc are empty or not.

IEnumerable<string> lines = File.ReadLines("target.txt");
if(lines.IsEmpty()) {
    Console.WriteLine("target.txt is empty.");
    return ;
}

// iterate all line and use it.

This is more clear and explicit than Any and ! usage. And beginner can notice the IsEmpty method with IntelliSense.

Relatives

There is IsEmpty method in Ix.NET.

Ix.NET

https://github.com/dotnet/reactive/blob/master/Ix.NET/Source/System.Interactive/Empty.cs

Next languages have IsEmpty or isEmpty methods.

F# https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/list.isempty['t]-function-[fsharp] https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/array.isempty['t]-function-[fsharp] https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/seq.isempty['t]-function-[fsharp]

Java https://docs.oracle.com/javase/10/docs/api/java/util/Collection.html#isEmpty()

Kotlin https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/is-empty.html https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-collection/is-empty.html

Scala https://www.scala-lang.org/api/current/scala/collection/GenTraversableOnce.html#isEmpty:Boolean

Update

Add Discussion : How about use !enumrable.Any()?