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| # What is it? 🚀 | ||
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| **PolySharp** provides generated, source-only polyfills for C# language features, to easily use all runtime-agnostic features downlevel. The package is distributed as a source generator, so that it will automatically detect which polyfills are needed depending on the target framework and project in use: just add a reference to **PolySharp**, set your C# language version to latest, and have fun! | ||
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| # TLDR? What is this for? ✨ | ||
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| Put simply: are you working on .NET Framework, or UWP, or some other older .NET runtime and still would like to use all the cool new features that C# 11 has? Well this library lets you do just that! It will generate for you all the "magic types" that the C# compiler needs to "see" in order for it to allow using new language features even if you're not using the latest framework out there. | ||
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| Here's an example of some of the new features that **PolySharp** can enable downlevel: | ||
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| > **Note**: not all the new C# features can be "tricked" this way (eg. those requiring runtime support, such as [static abstract members](https://learn.microsoft.com/dotnet/csharp/whats-new/tutorials/static-virtual-interface-members), still won't work). But almost everything else will (eg. nullability annotations, pattern matching, etc.), and this applies to a big number of new C# features. Try **PolySharp** out, don't get stuck on C# 6.0 or other older versions! 🎉 | ||
| > **Note**: use on .NET Framework 3.5 is particularly limited due to shortcomings of the BCL there. In particular, the `System.Range` type will not be generated unless `System.ValueTuple` is referenced (meaning that eg. list patterns won't work by default), and some features such as records will not be usable at all due to the C# compiler missing some necessary APIs that cannot be polifilled. All other features should work as expected. | ||
| # Documentation 📖 | ||
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| **PolySharp** includes the following polyfills: | ||
| - Nullability attributes (for [nullable reference types](https://learn.microsoft.com/dotnet/csharp/nullable-references)): | ||
| - `[AllowNull]` | ||
| - `[DisallowNull]` | ||
| - `[DoesNotReturn]` | ||
| - `[DoesNotReturnIf]` | ||
| - `[MaybeNull]` | ||
| - `[MaybeNullWhen]` | ||
| - `[MemberNotNull]` | ||
| - `[MemberNotNullWhen]` | ||
| - `[NotNull]` | ||
| - `[NotNullIfNotNull]` | ||
| - `[NotNullWhen]` | ||
| - `Index` and `Range` (see [indices and ranges](https://learn.microsoft.com/dotnet/csharp/whats-new/tutorials/ranges-indexes)) | ||
| - `[UnscopedRef]` (see [low-level struct improvements](https://github.com/dotnet/csharplang/blob/main/proposals/low-level-struct-improvements.md)) | ||
| - Required members (see [required modifier](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/required)) | ||
| - `[RequiredMember]` | ||
| - `[SetsRequiredMembers]` | ||
| - `[CompilerFeatureRequired]` (needed to support several features) | ||
| - `[IsExternalInit]` (needed for [init-only properties](https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/init)) | ||
| - `[SkipLocalsInit]` (see [docs](https://learn.microsoft.com/dotnet/csharp/language-reference/attributes/general#skiplocalsinit-attribute)) | ||
| - Interpolated string handlers (see [docs](https://learn.microsoft.com/dotnet/csharp/whats-new/tutorials/interpolated-string-handler)) | ||
| - `[InterpolatedStringHandler]` | ||
| - `[InterpolatedStringHandlerArgument]` | ||
| - `[CallerArgumentExpression]` (see [docs](https://learn.microsoft.com/dotnet/csharp/language-reference/proposals/csharp-10.0/caller-argument-expression)) | ||
| - `[RequiresPreviewFeatures]` (needed for [preview features](https://github.com/dotnet/designs/blob/main/accepted/2021/preview-features/preview-features.md)) | ||
| - `[AsyncMethodBuilder]` (needed for [custom method builder types](https://learn.microsoft.com/dotnet/csharp/language-reference/proposals/csharp-10.0/async-method-builders)) | ||
| - `[StringSyntax]` (needed to enable [syntax highlight in the IDE](https://github.com/dotnet/runtime/issues/62505)) | ||
| - `[ModuleInitializer]` (needed to enable [custom module initializers](https://learn.microsoft.com/dotnet/csharp/language-reference/proposals/csharp-9.0/module-initializers)) | ||
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| To leverage them, make sure to bump your C# language version. You can do this by setting the `<LangVersion>` MSBuild property in your project. For instance, by adding `<LangVersion>11.0</LangVersion>` (or your desired C# version) to the first `<PropertyGroup>` of your .csproj file. For more info on this, [see here](https://sergiopedri.medium.com/enabling-and-using-c-9-features-on-older-and-unsupported-runtimes-ce384d8debb), but remember that you don't need to manually copy polyfills anymore: simply adding a reference to **PolySharp** will do this for you automatically. | ||
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| It also includes the following optional runtime-supported polyfills: | ||
| - Reflection annotation attributes (see [docs](https://learn.microsoft.com/dotnet/core/deploying/trimming/prepare-libraries-for-trimming)): | ||
| - `[DynamicallyAccessedMembers]` | ||
| - `[DynamicDependency]` | ||
| - `[RequiresUnreferencedCode]` | ||
| - `[UnconditionalSuppressMessage]` | ||
| - `[StackTraceHidden]` (see [here](https://makolyte.com/csharp-exclude-exception-throw-helper-methods-from-the-stack-trace/)) | ||
| - `[UnmanagedCallersOnly]` (see [docs](https://learn.microsoft.com/dotnet/api/system.runtime.interopservices.unmanagedcallersonlyattribute))) | ||
| - Platform support annotation attributes (see [docs](https://learn.microsoft.com/dotnet/standard/analyzers/platform-compat-analyzer)): | ||
| - `[ObsoletedOSPlatform]` | ||
| - `[SupportedOSPlatform]` | ||
| - `[SupportedOSPlatformGuard]` | ||
| - `[TargetPlatform]` | ||
| - `[UnsupportedOSPlatform]` | ||
| - `[UnsupportedOSPlatformGuard]` | ||
| - `[SuppressGCTransition]` (see [here](https://devblogs.microsoft.com/dotnet/improvements-in-native-code-interop-in-net-5-0/)) | ||
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| # Options ⚙️ | ||
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| **PolySharp**'s generation can be configured through some MSBuild properties to set in consuming projects. | ||
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| The following properties are available: | ||
| - "PolySharpUsePublicAccessibilityForGeneratedTypes": makes all generated types public. | ||
| - "PolySharpIncludeRuntimeSupportedAttributes": enables polyfills for (dummy) runtime-supported attributes too. | ||
| - "PolySharpExcludeGeneratedTypes": excludes specific types from generation (';' or ',' separated type names). | ||
| - "PolySharpIncludeGeneratedTypes": only includes specific types for generation (';' or ',' separated type names). |