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Is Dotnet Standard 2.0 Compat free to use?

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Who published Dotnet Standard 2.0 Compat?

stevenfackley (@stevenfackley) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Dotnet Standard 2.0 Compat by stevenfackley

Name: Dotnet Standard 2.0 Compat
Author: stevenfackley

Dotnet Standard 2.0 Compat

Use when writing or contributing to .NET code that must target .NET Standard 2.0 — often multi-targeted with .NET 10 in shared libraries. Lists what is NOT available on the ns2.0 floor so you don't put .NET 10-only APIs in code that must compile for both.

File contents

.NET Standard 2.0 Compatibility Guardrail

Shared libraries commonly multi-target netstandard2.0;net10.0 — ns2.0 for reach (.NET Framework 4.6.1+, Xamarin, Unity, older runtimes), net10.0 for modern features. Code in the shared (non-#if'd) path must compile for the ns2.0 floor. A constrained model will reach for net10-only APIs and break the ns2.0 build.

Detect first

Read the .csproj. <TargetFrameworks>netstandard2.0;net10.0</TargetFrameworks> = dual floor. Anything outside an #if NET block must be ns2.0-safe.

NOT available on ns2.0 (net-only) — don't use in shared code

DateOnly / TimeOnly (net6+), Half (net5+), Int128/UInt128, generic math + static abstract interface members (net7+).
Default interface methods (ns2.1 / .NET Core 3+ runtime feature).
required members (C# 11) and record/init accessors — compile on ns2.0 ONLY with polyfill attributes (IsExternalInit, RequiredMemberAttribute, CompilerFeatureRequiredAttribute).
[CallerArgumentExpression] and some nullable attributes — need polyfills.

In-box on net, but NEEDS A NuGet PACKAGE on ns2.0

System.Text.Json → add the System.Text.Json package.
Span<T> / Memory<T> → System.Memory.
IAsyncEnumerable<T> / IAsyncDisposable / await foreach → Microsoft.Bcl.AsyncInterfaces.
ValueTask extras → System.Threading.Tasks.Extensions.

Safe on ns2.0

async/await, Task<T>, LINQ, generics, most System.* collections/strings/IO, HttpClient.
Compiler-level C# features: nullable reference type ANNOTATIONS (<Nullable>enable</Nullable> + LangVersion), pattern matching, tuples, local functions, file-scoped namespaces.

Patterns that work

Polyfills: add PolySharp (source-only) or a tiny IsExternalInit/RequiredMember shim so you can use record/init/required while still targeting ns2.0.
Gate modern code: #if NET8_0_OR_GREATER … #else … #endif for net-only fast paths.
Turn on <Nullable>enable</Nullable> even on the ns2.0 floor — annotations cost nothing and catch bugs.

Verify, don't guess

Unsure if an API exists on ns2.0? Check the API reference at learn.microsoft.com/dotnet/api with the version selector set to netstandard-2.0.

---name: dotnet-standard-2-0-compatdescription: Use when writing or contributing to .NET code that must target .NET Standard 2.0 — often multi-targeted with .NET 10 in shared libraries. Lists what is NOT available on the ns2.0 floor so you don't put .NET 10-only APIs in code that must compile for both.---# .NET Standard 2.0 Compatibility GuardrailShared libraries commonly multi-target `netstandard2.0;net10.0` — ns2.0 for reach (.NET Framework4.6.1+, Xamarin, Unity, older runtimes), net10.0 for modern features. **Code in the shared(non-`#if`'d) path must compile for the ns2.0 floor.** A constrained model will reach fornet10-only APIs and break the ns2.0 build.## Detect firstRead the `.csproj`. `<TargetFrameworks>netstandard2.0;net10.0</TargetFrameworks>` = dual floor.Anything outside an `#if NET` block must be ns2.0-safe.## NOT available on ns2.0 (net-only) — don't use in shared code- `DateOnly` / `TimeOnly` (net6+), `Half` (net5+), `Int128`/`UInt128`, generic math + static abstract interface members (net7+).- Default interface methods (ns2.1 / .NET Core 3+ runtime feature).- `required` members (C# 11) and `record`/`init` accessors — compile on ns2.0 ONLY with polyfill attributes (`IsExternalInit`, `RequiredMemberAttribute`, `CompilerFeatureRequiredAttribute`).- `[CallerArgumentExpression]` and some nullable attributes — need polyfills.## In-box on net, but NEEDS A NuGet PACKAGE on ns2.0- `System.Text.Json` → add the `System.Text.Json` package.- `Span<T>` / `Memory<T>` → `System.Memory`.- `IAsyncEnumerable<T>` / `IAsyncDisposable` / `await foreach` → `Microsoft.Bcl.AsyncInterfaces`.- `ValueTask` extras → `System.Threading.Tasks.Extensions`.## Safe on ns2.0- `async`/`await`, `Task<T>`, LINQ, generics, most `System.*` collections/strings/IO, `HttpClient`.- Compiler-level C# features: nullable reference type ANNOTATIONS (`<Nullable>enable</Nullable>` + `LangVersion`), pattern matching, tuples, local functions, file-scoped namespaces.## Patterns that work- **Polyfills:** add `PolySharp` (source-only) or a tiny `IsExternalInit`/`RequiredMember` shim so you can use `record`/`init`/`required` while still targeting ns2.0.- **Gate modern code:** `#if NET8_0_OR_GREATER … #else … #endif` for net-only fast paths.- Turn on `<Nullable>enable</Nullable>` even on the ns2.0 floor — annotations cost nothing and catch bugs.## Verify, don't guessUnsure if an API exists on ns2.0? Check the API reference at learn.microsoft.com/dotnet/api withthe version selector set to **netstandard-2.0**.

Frequently asked questions