Building a library on the SDK¶

This page covers libraries that build on the SDK, such as a shared set of host tools or a module, and why they should target the same frameworks as the SDK.

Target netstandard2.0 and net8.0¶

Build your library for both of the SDK's targets:

<PropertyGroup>
  <TargetFrameworks>netstandard2.0;net8.0</TargetFrameworks>
</PropertyGroup>

A library on Faden.UI.Wpf targets net472 and net8.0-windows for the same reason.

Why both¶

The SDK's types use init setters: its records, MessageAttachment, the options classes. In the netstandard2.0 build, these setters are compiled against a different marker type than in the net8.0 build, so their signatures differ between the two builds.

A library built for netstandard2.0 only is compiled against the SDK's netstandard2.0 build. A .NET 8 or later application that loads it gets the SDK's net8.0 build, and the library's calls to those setters fail at run time with MissingMethodException.

Built for both targets, each application loads matching builds: a .NET 8 or later application gets the net8.0 builds of your library and the SDK, and a .NET Framework host gets the netstandard2.0 builds of both.

The same applies to streaming. A netstandard2.0 build that uses IAsyncEnumerable<T>, as anything that reads StreamAsync does, depends on the Microsoft.Bcl.AsyncInterfaces package, which the .NET 10 SDK may prune from a .NET application's package graph. The library then fails to load in that application. Its net8.0 build has no such dependency.

Records and init setters in your own code¶

If your library declares records or init setters itself, its netstandard2.0 build needs the IsExternalInit marker type, which netstandard2.0 does not have. Declare it once, for that target only:

#if NETSTANDARD2_0
namespace System.Runtime.CompilerServices
{
    internal static class IsExternalInit
    {
    }
}
#endif

This is what the SDK does itself.