Is IAsyncEnumerable supported in C# 8.0?

Question

Its really hard to find any information on IAsyncEnumerable, other than a few mentions in the 'What's New c# 8.0' articles. Trying to use it in Visual Studio 2019 with netstandard 2.0 and C# 8 enabled, it does recognize the class but i get a ton of errors on build:

Intersperse

are there images of error messages? – Johannajohannah

C# 8 supports those things, but doesn't define them. You need to target a release of .NET that does, which, at the moment, is only the preview release of .NET Core 3.0. – Dingdong

Answer 1

C# 8 supports these features. However, this wont work with .Net standard 2.0

IAsyncEnumerable Interface

Applies to

.NET Core 3.0 Preview 3

.NET Standard 2.1 Preview

You will have to get either one of the previews.

You can find more information on .Net Core 3 Preview here

• https://devblogs.microsoft.com/dotnet/announcing-net-core-3-preview-4/

• https://dotnet.microsoft.com/download/dotnet-core/3.0

Hent

So just a heads up for anyone planning on trying this, unfortunately it wont work if you use Net Core 3.0 along with EntityframeworkCore, because of the following error: Error CS0433 The type 'IAsyncEnumerable<T>' exists in both 'System.Interactive.Async, Version=3.2.0.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' and 'System.Runtime, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' – Intersperse

Just ran into the above comment myself. Was trying to try out IAsyncEnumerable with providing a InMemory database for data but nope! Dreams crushed. – Pellagra

Answer 2

The answer of Vlad is the right one.

1. Add LangVersion 8.0 to the desired Projects PropertGroup
2. Add the Microsoft.Bcl.AsyncInterfaces as PackageReference

For example: MyDummyLib.csproj

<PropertyGroup>
    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
    <LangVersion>8.0</LangVersion>
    <AssemblyName>MyDummyLib</AssemblyName>
    <RootNamespace>MyDummyLib</RootNamespace>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
</PropertyGroup>

<ItemGroup Condition="'$(TargetFramework)'=='netstandard2.0'">
    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="1.1.1" />
</ItemGroup>

Liberty

Answer 3

For .NET Standard 2.0 you should install Microsoft.Bcl.AsyncInterfaces

https://www.nuget.org/packages/Microsoft.Bcl.AsyncInterfaces/

Inflationism

Please don't just post some tool or library as an answer. At least demonstrate how it solves the problem in the answer itself. – Gerhard

Since the problem is about missing member IAsyncEnumerable .NET Standard 2.0 - this packet publishied by Microsoft for compatibility in .NET Standard 2.0. You don't need do anything acept install it. – Inflationism

Answer 4

Looks like you need to target .NET Standard 2.1 but it’s still only in preview.

https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.iasyncenumerable-1?view=netstandard-2.1

Quadrennial