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NetEscapades.EnumGenerators

Build status NuGet

A Source Generator package that generates extension methods for enums, to allow fast "reflection".

This source generator requires the .NET 7 SDK. You can target earlier frameworks like .NET Core 3.1 etc, but the SDK must be at least 7.0.100

Add the package to your application using

dotnet add package NetEscapades.EnumGenerators

This adds a <PackageReference> to your project. You can additionally mark the package as PrivateAssets="all" and ExcludeAssets="runtime".

Setting PrivateAssets="all" means any projects referencing this one won't get a reference to the NetEscapades.EnumGenerators package. Setting ExcludeAssets="runtime" ensures the NetEscapades.EnumGenerators.Attributes.dll file is not copied to your build output (it is not required at runtime).

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
  </PropertyGroup>

  <!-- Add the package -->
  <PackageReference Include="NetEscapades.EnumGenerators" Version="1.0.0-beta11" 
    PrivateAssets="all" ExcludeAssets="runtime" />
  <!-- -->

</Project>

Adding the package will automatically add a marker attribute, [EnumExtensions], to your project.

To use the generator, add the [EnumExtensions] attribute to an enum. For example:

[EnumExtensions]
public enum MyEnum
{
    First,

    [Display(Name = "2nd")]
    Second,
}

This will generate a class called MyEnumExtensions (by default), which contains a number of helper methods. For example:

public static partial class MyEnumExtensions
{
    public const int Length = 2;

    public static string ToStringFast(this MyEnum value)
        => value switch
        {
            MyEnum.First => nameof(MyEnum.First),
            MyEnum.Second => "2nd",
            _ => value.ToString(),
        };

   public static bool IsDefined(MyEnum value)
        => value switch
        {
            MyEnum.First => true,
            MyEnum.Second => true,
            _ => false,
        };

    public static bool IsDefined(string name)
        => name switch
        {
            nameof(MyEnum.First) => true,
            nameof(MyEnum.Second) => true,
            _ => false,
        };

    public static bool TryParse(
        [System.Diagnostics.CodeAnalysis.NotNullWhen(true)] string? name, 
        bool ignoreCase, 
        out MyEnum value)
        => ignoreCase ? TryParseIgnoreCase(name, out value) : TryParse(name, out value);

    private static bool TryParseIgnoreCase(
        [System.Diagnostics.CodeAnalysis.NotNullWhen(true)] string? name, 
        out MyEnum value)
    {
        switch (name)
        {
            case { } s when s.Equals(nameof(MyEnum.First), System.StringComparison.OrdinalIgnoreCase):
                value = MyEnum.First;
                return true;
            case { } s when s.Equals(nameof(MyEnum.Second), System.StringComparison.OrdinalIgnoreCase):
                value = MyEnum.Second;
                return true;
            case { } s when int.TryParse(name, out var val):
                value = (MyEnum)val;
                return true;
            default:
                value = default;
                return false;
        }
    }

    public static bool TryParse(
        [System.Diagnostics.CodeAnalysis.NotNullWhen(true)] string? name, 
        out MyEnum value)
    {
        switch (name)
        {
            case nameof(MyEnum.First):
                value = MyEnum.First;
                return true;
            case nameof(MyEnum.Second):
                value = MyEnum.Second;
                return true;
            case { } s when int.TryParse(name, out var val):
                value = (MyEnum)val;
                return true;
            default:
                value = default;
                return false;
        }
    }

    public static MyEnum[] GetValues()
    {
        return new[]
        {
            MyEnum.First,
            MyEnum.Second,
        };
    }

    public static string[] GetNames()
    {
        return new[]
        {
            nameof(MyEnum.First),
            nameof(MyEnum.Second),
        };
    }
}

If you create a "Flags" enum by decorating it with the [Flags] attribute, an additional method is created, which provides a bitwise alternative to the Enum.HasFlag(flag) method:

public static bool HasFlagFast(this MyEnum value, MyEnum flag)
    => flag == 0 ? true : (value & flag) == flag;

Note that if you provide a [Display] or [Description] attribute, the value you provide for this attribute can be used by methods like ToStringFast() and TryParse() by passing the argument allowMatchingMetadataAttribute: true. Adding both attributes to an enum member is not supported, though conventionally the "first" attribute will be used.

You can override the name of the extension class by setting ExtensionClassName in the attribute and/or the namespace of the class by setting ExtensionClassNamespace. By default, the class will be public if the enum is public, otherwise it will be internal.

Enabling interception

Interceptors were introduced as an experimental feature in C#12 with .NET 8. They allow a source generator to "intercept" certain method calls, and replace the call with a different one. NetEscapades.EnumGenerators has support for intercepting ToString() and HasFlag() method calls.

To use interceptors, you must be using at least version 8.0.400 of the .NET SDK. This ships with Visual Studio version 17.11, so you will need at least that version or higher.

To enable interception for a project, update to the latest version of NetEscapades.EnumGenerators and set the EnableEnumGeneratorInterceptor property in your .csproj to true:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <!-- 👇 Add this property to enable the interceptor in the project -->
    <EnableEnumGeneratorInterceptor>true</EnableEnumGeneratorInterceptor>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="NetEscapades.EnumGenerators" Version="1.0.0-beta11" 
    PrivateAssets="all" ExcludeAssets="runtime" />
  </ItemGroup>

</Project>

This enables interception for all enums defined in the project that use the [EnumExtensions] or [EnumExtensions<T>] attributes. If you wish to intercept calls made to enums with extensions defined in other projects, you must add the [Interceptable<T>] attribute in the project where you want the interception to happen, e.g.

[assembly:Interceptable<DateTimeKind>]
[assembly:Interceptable<Color>]

If you don't want a specific enum to be intercepted, you can set the IsInterceptable property to false, e.g.

[EnumExtensions(IsInterceptable = false)]
public enum Colour
{
    Red = 0,
    Blue = 1,
}

Interception only works when the target type is unambiguously an interceptable enum, so it won't work

  • When ToString() is called in other source generated code.
  • When ToString() is called in already-compiled code.
  • If the ToString() call is implicit (for example in string interpolation)
  • If the ToString() call is made on a base type, such as System.Enum or object
  • If the ToString() call is made on a generic type

Embedding the attributes in your project

By default, the [EnumExtensions] attributes referenced in your application are contained in an external dll. It is also possible to embed the attributes directly in your project, so they appear in the dll when your project is built. If you wish to do this, you must do two things:

  1. Define the MSBuild constant NETESCAPADES_ENUMGENERATORS_EMBED_ATTRIBUTES. This ensures the attributes are embedded in your project
  2. Add compile to the list of excluded assets in your <PackageReference> element. This ensures the attributes in your project are referenced, instead of the NetEscapades.EnumGenerators.Attributes.dll library.

Your project file should look something like this:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net7.0</TargetFramework>
    <!--  Define the MSBuild constant    -->
    <DefineConstants>$(DefineConstants);NETESCAPADES_ENUMGENERATORS_EMBED_ATTRIBUTES</DefineConstants>
  </PropertyGroup>

  <!-- Add the package -->
  <PackageReference Include="NetEscapades.EnumGenerators" Version="1.0.0-beta11" 
                    PrivateAssets="all"
                    ExcludeAssets="compile;runtime" />
<!--                               ☝ Add compile to the list of excluded assets. -->

</Project>

Preserving usages of the [EnumExtensions] attribute

The [EnumExtensions] attribute is decorated with the [Conditional] attribute, so their usage will not appear in the build output of your project. If you use reflection at runtime on one of your enums, you will not find [EnumExtensions] in the list of custom attributes.

If you wish to preserve these attributes in the build output, you can define the NETESCAPADES_ENUMGENERATORS_USAGES MSBuild variable. Note that this means your project will have a runtime-dependency on NetEscapades.EnumGenerators.Attributes.dll so you need to ensure this is included in your build output.

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <!--  Define the MSBuild constant to preserve usages   -->
    <DefineConstants>$(DefineConstants);NETESCAPADES_ENUMGENERATORS_USAGES</DefineConstants>
  </PropertyGroup>

  <!-- Add the package -->
  <PackageReference Include="NetEscapades.EnumGenerators" Version="1.0.0-beta11" PrivateAssets="all" />
  <!--              ☝ You must not exclude the runtime assets in this case -->

</Project>

Error CS0436 and [InternalsVisibleTo]

In the latest version of NetEscapades.EnumGenerators, you should not experience error CS0436 by default.

In previous versions of the NetEscapades.EnumGenerators generator, the [EnumExtensions] attributes were added to your compilation as internal attributes by default. If you added the source generator package to multiple projects, and used the [InternalsVisibleTo] attribute, you could experience errors when you build:

warning CS0436: The type 'EnumExtensionsAttribute' in 'NetEscapades.EnumGenerators\NetEscapades.EnumGenerators\EnumExtensionsAttribute.cs' conflicts with the imported type 'EnumExtensionsAttribute' in 'MyProject, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

In the latest version of NetEscapades.EnumGenerators, the attributes are not embedded by default, so you should not experience this problem. If you see this error, compare your installation to the examples in the installation guide.