Polyfill

Source only package that exposes newer .NET and C# features to older runtimes.

The package targets netstandard2.0 and is designed to support the following runtimes.

net461, net462, net47, net471, net472, net48, net481
netcoreapp2.0, netcoreapp2.1, netcoreapp3.0, netcoreapp3.1
net5.0, net6.0, net7.0, net8.0

See Milestones for release notes.

Nuget

https://nuget.org/packages/Polyfill/

SDK / LangVersion

This project uses features from the current stable SDK and C# language. As such consuming projects should target those:

LangVersion

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <LangVersion>latest</LangVersion>

global.json

{
  "sdk": {
    "version": "7.0.306",
    "rollForward": "latestFeature"
  }
}

Consuming and type visibility

The default type visibility for all polyfills is internal. This means it can be consumed in multiple projects and types will not conflict.

Consuming in an app

If Polyfill is being consumed in a solution that produce an app, then it is recommended to use the Polyfill nuget only in the root "app project" and enable PolyPublic.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <PolyPublic>true</PolyPublic>

Then all consuming projects, like tests, will not need to use the Polyfill nuget.

Consuming in a library

If Polyfill is being consumed in a solution that produce a library (and usually a nuget), then the Polyfill nuget can be added to all projects.

If, however, InternalsVisibleTo is being used to expose APIs (for example to test projects), then the Polyfill nuget should be added only to the root library project.

Included polyfills

ModuleInitializerAttribute

ModuleInitializerAttribute

Reference: Module Initializers

static bool InitCalled;

[Test]
public void ModuleInitTest() =>
    Assert.True(InitCalled);

[ModuleInitializer]
public static void ModuleInit() =>
    InitCalled = true;

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IsExternalInit

Reference: init (C# Reference)

class InitExample
{
    public int Member { get; init; }
}

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Nullable attributes

Reference: Nullable reference types

Required attributes

Reference: C# required modifier

public class Person
{
    public Person() { }

    [SetsRequiredMembers]
    public Person(string name) =>
        Name = name;

    public required string Name { get; init; }
}

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CompilerFeatureRequiredAttribute

CompilerFeatureRequiredAttribute

Indicates that compiler support for a particular feature is required for the location where this attribute is applied.

SkipLocalsInit

SkipLocalsInitAttribute

Reference: (SkipLocalsInit attribute)(https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/attributes/general#skiplocalsinit-attribute)

the SkipLocalsInit attribute prevents the compiler from setting the .locals init flag when emitting to metadata. The SkipLocalsInit attribute is a single-use attribute and can be applied to a method, a property, a class, a struct, an interface, or a module, but not to an assembly. SkipLocalsInit is an alias for SkipLocalsInitAttribute.

class SkipLocalsInitSample
{
    [SkipLocalsInit]
    static void ReadUninitializedMemory()
    {
        Span<int> numbers = stackalloc int[120];
        for (var i = 0; i < 120; i++)
        {
            Console.WriteLine(numbers[i]);
        }
    }
}

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Index and Range

Reference: Indices and ranges

If consuming in a project that targets net461 or net462, a reference to System.ValueTuple is required. See References: System.ValueTuple.

[TestFixture]
class IndexRangeSample
{
    [Test]
    public void Range()
    {
        var substring = "value"[2..];
        Assert.AreEqual("lue", substring);
    }

    [Test]
    public void Index()
    {
        var ch = "value"[^2];
        Assert.AreEqual('u', ch);
    }
}

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UnscopedRefAttribute

UnscopedRefAttribute

Reference: Low Level Struct Improvements

#if !NET7_0_OR_GREATER

using System.Diagnostics.CodeAnalysis;

struct UnscopedRefUsage
{
    int field;

    [UnscopedRef] ref int Prop1 => ref field;
}

#endif

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CallerArgumentExpressionAttribute

CallerArgumentExpressionAttribute

Reference: CallerArgumentExpression

using System.IO;

static class Guard
{
    public static void FileExists(string path, [CallerArgumentExpression("path")] string argumentName = "")
    {
        if (!File.Exists(path))
        {
            throw new ArgumentException($"File not found. Path: {path}", argumentName);
        }
    }
}

static class GuardUsage
{
    public static string[] Method(string path)
    {
        Guard.FileExists(path);
        return File.ReadAllLines(path);
    }
}

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Extensions

The class PolyfillExtensions includes the following extension methods:

Boolean

Boolean TryFormat(Span<Char>, Int32&) reference

Byte

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Dictionary<TKey,TValue>

Boolean Remove<TKey, TValue>(TKey, TValue&) reference

IEnumerable

IEnumerable<TSource[]> Chunk<TSource>(Int32) reference
IEnumerable<TSource> Except<TSource>(TSource) reference
IEnumerable<TSource> Except<TSource>(TSource[]) reference
IEnumerable<TSource> Except<TSource>(TSource, IEqualityComparer<TSource>) reference
IEnumerable<TSource> Except<TSource>(IEqualityComparer<TSource>, TSource[]) reference
TSource MaxBy<TSource, TKey>(Func<TSource,TKey>) reference
TSource MaxBy<TSource, TKey>(Func<TSource,TKey>, IComparer<TKey>) reference
TSource MinBy<TSource, TKey>(Func<TSource,TKey>) reference
TSource MinBy<TSource, TKey>(Func<TSource,TKey>, IComparer<TKey>) reference
IEnumerable<TSource> SkipLast<TSource>(Int32) reference

IReadOnlyDictionary<TKey,TValue>

TValue GetValueOrDefault<TKey, TValue>(TKey) reference
TValue GetValueOrDefault<TKey, TValue>(TKey, TValue) reference

KeyValuePair<TKey,TValue>

Void Deconstruct<TKey, TValue>(TKey&, TValue&) reference

DateTime

DateTime AddMicroseconds(Double) reference
Int32 Microsecond() reference
Int32 Nanosecond() reference
Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

DateTimeOffset

DateTimeOffset AddMicroseconds(Double) reference
Int32 Microsecond() reference
Int32 Nanosecond() reference
Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Decimal

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Process

Task WaitForExitAsync(CancellationToken) reference

Double

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Int16

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Int32

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Int64

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Stream

Task CopyToAsync(Stream, CancellationToken) reference
ValueTask<Int32> ReadAsync(Memory<Byte>, CancellationToken) reference
ValueTask WriteAsync(ReadOnlyMemory<Byte>, CancellationToken) reference

TextReader

ValueTask<Int32> ReadAsync(Memory<Char>, CancellationToken) reference
Task<String> ReadLineAsync(CancellationToken) reference
Task<String> ReadToEndAsync(CancellationToken) reference

TextWriter

Void Write(ReadOnlySpan<Char>) reference
ValueTask WriteAsync(ReadOnlyMemory<Char>, CancellationToken) reference
Void WriteLine(ReadOnlySpan<Char>) reference
ValueTask WriteLineAsync(ReadOnlyMemory<Char>, CancellationToken) reference

HttpClient

Task<Byte[]> GetByteArrayAsync(String, CancellationToken) reference
Task<Byte[]> GetByteArrayAsync(Uri, CancellationToken) reference
Task<Stream> GetStreamAsync(String, CancellationToken) reference
Task<Stream> GetStreamAsync(Uri, CancellationToken) reference
Task<String> GetStringAsync(String, CancellationToken) reference
Task<String> GetStringAsync(Uri, CancellationToken) reference

HttpContent

Task<Byte[]> ReadAsByteArrayAsync(CancellationToken) reference
Task<Stream> ReadAsStreamAsync(CancellationToken) reference
Task<String> ReadAsStringAsync(CancellationToken) reference

ReadOnlySpan

Boolean EndsWith(String, StringComparison) reference
Boolean SequenceEqual(String) reference
Boolean StartsWith(String, StringComparison) reference

ReadOnlySpan

Boolean Contains<T>(T) reference

Reflection.EventInfo

Reflection.NullabilityState GetNullability()
Reflection.NullabilityInfo GetNullabilityInfo()
Boolean IsNullable()

Reflection.FieldInfo

Reflection.NullabilityState GetNullability()
Reflection.NullabilityInfo GetNullabilityInfo()
Boolean IsNullable()

Reflection.MemberInfo

Reflection.NullabilityState GetNullability()
Reflection.NullabilityInfo GetNullabilityInfo()
Boolean HasSameMetadataDefinitionAs(Reflection.MemberInfo) reference
Boolean IsNullable()

Reflection.ParameterInfo

Reflection.NullabilityState GetNullability()
Reflection.NullabilityInfo GetNullabilityInfo()
Boolean IsNullable()

Reflection.PropertyInfo

Reflection.NullabilityState GetNullability()
Reflection.NullabilityInfo GetNullabilityInfo()
Boolean IsNullable()

SByte

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Single

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

Span

Boolean EndsWith(String) reference
Boolean SequenceEqual(String) reference
Boolean StartsWith(String) reference

Span

Boolean Contains<T>(T) reference

String

Boolean Contains(String, StringComparison) reference
Boolean Contains(Char) reference
Void CopyTo(Span<Char>) reference
Boolean EndsWith(Char) reference
Int32 GetHashCode(StringComparison) reference
String[] Split(Char, StringSplitOptions) reference
String[] Split(Char, Int32, StringSplitOptions) reference
Boolean StartsWith(Char) reference
Boolean TryCopyTo(Span<Char>) reference

StringBuilder

StringBuilder Append(ReadOnlySpan<Char>) reference
StringBuilder Append(AppendInterpolatedStringHandler&) reference
StringBuilder Append(IFormatProvider, AppendInterpolatedStringHandler&) reference
StringBuilder AppendLine(AppendInterpolatedStringHandler&) reference
StringBuilder AppendLine(IFormatProvider, AppendInterpolatedStringHandler&) reference
Void CopyTo(Int32, Span<Char>, Int32) reference
Boolean Equals(ReadOnlySpan<Char>) reference

Important

The methods using AppendInterpolatedStringHandler parameter are not extensions because the compiler prefers to use the overload with string parameter instead.

CancellationToken

CancellationTokenRegistration Register(Action<Object,CancellationToken>, Object) reference
CancellationTokenRegistration UnsafeRegister(Action<Object>, Object) reference
CancellationTokenRegistration UnsafeRegister(Action<Object,CancellationToken>, Object) reference

CancellationTokenSource

Task CancelAsync() reference

Task

Task WaitAsync(CancellationToken) reference
Task WaitAsync(TimeSpan) reference
Task WaitAsync(TimeSpan, CancellationToken) reference

Task

Task<TResult> WaitAsync<TResult>(CancellationToken) reference
Task<TResult> WaitAsync<TResult>(TimeSpan) reference
Task<TResult> WaitAsync<TResult>(TimeSpan, CancellationToken) reference

TimeSpan

Int32 Microseconds() reference
Int32 Nanoseconds() reference

Type

Boolean IsGenericMethodParameter() reference

UInt16

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

UInt32

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

UInt64

Boolean TryFormat(Span<Char>, Int32&, ReadOnlySpan<Char>, IFormatProvider) reference

References

If any of the below reference are not included, the related polyfills will be disabled.

System.ValueTuple

If consuming in a project that targets net461 or net462, a reference to System.ValueTuple nuget is required.

<PackageReference Include="System.ValueTuple"
                  Version="4.5.0"
                  Condition="$(TargetFramework.StartsWith('net46'))" />

System.Memory

If using Span APIs and consuming in a project that targets netstandard, netframework, or netcoreapp2*, a reference to System.Memory nuget is required.

<PackageReference Include="System.Memory"
                  Version="4.5.5"
                  Condition="$(TargetFrameworkIdentifier) == '.NETStandard' or
                             $(TargetFrameworkIdentifier) == '.NETFramework' or
                             $(TargetFramework.StartsWith('netcoreapp2'))" />

System.Threading.Tasks.Extensions

If using ValueTask APIs and consuming in a project that target netframework, netstandard2, or 'netcoreapp2', a reference to System.Threading.Tasks.Extensions nuget is required.

<PackageReference Include="System.Threading.Tasks.Extensions"
                  Version="4.5.4"
                  Condition="$(TargetFramework) == 'netstandard2.0' or
                             $(TargetFramework) == 'netcoreapp2.0' or
                             $(TargetFrameworkIdentifier) == '.NETFramework'" />

Nullability

Example target class

Given the following class

class NullabilityTarget
{
    public string? StringField;
    public string?[] ArrayField;
    public Dictionary<string, object?> GenericField;
}

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NullabilityInfoContext

[Test]
public void Test()
{
    var type = typeof(NullabilityTarget);
    var arrayField = type.GetField("ArrayField")!;
    var genericField = type.GetField("GenericField")!;

    var context = new NullabilityInfoContext();

    var arrayInfo = context.Create(arrayField);

    Assert.AreEqual(NullabilityState.NotNull, arrayInfo.ReadState);
    Assert.AreEqual(NullabilityState.Nullable, arrayInfo.ElementType!.ReadState);

    var genericInfo = context.Create(genericField);

    Assert.AreEqual(NullabilityState.NotNull, genericInfo.ReadState);
    Assert.AreEqual(NullabilityState.NotNull, genericInfo.GenericTypeArguments[0].ReadState);
    Assert.AreEqual(NullabilityState.Nullable, genericInfo.GenericTypeArguments[1].ReadState);
}

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NullabilityInfoExtensions

NullabilityInfoExtensions provides static and thread safe wrapper around NullabilityInfoContext. It adds three extension methods to each of ParameterInfo, PropertyInfo, EventInfo, and FieldInfo.

GetNullabilityInfo: returns the NullabilityInfo for the target info.
GetNullability: returns the NullabilityState for the state (NullabilityInfo.ReadState or NullabilityInfo.WriteState depending on which has more info) of target info.
IsNullable: given the state (NullabilityInfo.ReadState or NullabilityInfo.WriteState depending on which has more info) of the info:
- Returns true if state is NullabilityState.Nullable.
- Returns false if state is NullabilityState.NotNull.
- Throws an exception if state is NullabilityState.Unknown.

Alternatives

PolySharp

https://github.com/Sergio0694/PolySharp

Combination of

Reason this project was created instead of using the above

PolySharp uses c# source generators. In my opinion a "source-only package" implementation is better because:

Simpler implementation
Easier to debug if something goes wrong.
Uses less memory at compile time. Since there is no source generator assembly to load.
Faster at compile time. Since no source generator is required to execute.

The combination of the other 3 packages is not ideal because:

Required multiple packages to be referenced.
Does not cover all the scenarios included in this package.

Icon

Crack designed by Adrien Coquet from The Noun Project.

Polyfill

Nuget

SDK / LangVersion

LangVersion

global.json

Consuming and type visibility

Consuming in an app

Consuming in a library

Included polyfills

ModuleInitializerAttribute

IsExternalInit

Nullable attributes

Required attributes

CompilerFeatureRequiredAttribute

SkipLocalsInit

Index and Range

UnscopedRefAttribute

CallerArgumentExpressionAttribute

InterpolatedStringHandler

StringSyntaxAttribute

Trimming annotation attributes

Platform compatibility

StackTraceHiddenAttribute

UnmanagedCallersOnly

SuppressGCTransition

DisableRuntimeMarshalling

Extensions

Boolean

Byte

Dictionary<TKey,TValue>

IEnumerable

IReadOnlyDictionary<TKey,TValue>

KeyValuePair<TKey,TValue>

DateTime

DateTimeOffset

Decimal

Process

Double

Int16

Int32

Int64

Stream

TextReader

TextWriter

HttpClient

HttpContent

ReadOnlySpan

ReadOnlySpan

Reflection.EventInfo

Reflection.FieldInfo

Reflection.MemberInfo

Reflection.ParameterInfo

Reflection.PropertyInfo

SByte

Single

Span

Span

String

StringBuilder

CancellationToken

CancellationTokenSource

Task

Task

TimeSpan

Type

UInt16

UInt32

UInt64

References

System.ValueTuple

System.Memory

System.Threading.Tasks.Extensions

Nullability

Example target class

NullabilityInfoContext

NullabilityInfoExtensions

Alternatives

PolySharp

Combination of

Reason this project was created instead of using the above