A source generator that generates Match
methods for all your discriminated unions needs. ✨
Add <ProjectReference Include="Funcky.DiscriminatedUnion" Version="..." PrivateAssets="all" />
to your project file.
Apply the [DiscriminatedUnion]
to an abstract class (or record) with nested types representing the variants.
using Funcky;
var result = Result<int>.Ok(42);
var resultOrFallback = result.Match(ok: ok => ok.Value, error: _ => 0);
[DiscriminatedUnion]
public abstract partial record Result<T>
where T : notnull
{
public sealed partial record Ok(T Value) : Result<T>;
public sealed partial record Error(Exception Exception) : Result<T>;
}
- Visual Studio 2022
- Roslyn 4.0.0
- .NET 6
The attribute allows configuration of some aspects of source generation.
The auto-generated Match
and Switch
methods are public by default.
When NonExhaustive
is set to true
, these methods are generated with internal
visibility instead.
The auto-generated Match
method uses a generic type for the result. This type is named TResult
by default.
This can cause conflict with generic types on the discriminated union itself. Use MatchResultTypeName
to set a custom name for this type.
using Funcky;
[DiscriminatedUnion(MatchResultTypeName = "TMatchResult")]
public abstract partial record Result<TResult> { ... }
// Generated code
partial record Result<TResult>
{
public abstract TMatchResult Match<TMatchResult>(...);
...
}
The auto-generated Match
and Switch
methods only accept one level of inheritance by default.
Set Flatten
to true
to include arbitrarily deep inherited types in these methods.
using Funcky;
SyntaxNode node = ...;
var nodeAsString = node.Match(
keyword: keyword => keyword.Value,
integer: integer => integer.Value.ToString(),
double: @double => @double.Value.ToString());
[DiscriminatedUnion(Flatten = true)]
public abstract partial record SyntaxNode
{
public sealed partial record Keyword(string Value) : SyntaxNode;
public abstract partial record Literal : SyntaxNode;
public abstract partial record Number : Literal;
public sealed partial record Integer(int Value) : Number;
public sealed partial record Double(double Value) : Number;
}
System.Text.Json adds support for serializing derived classes starting with .NET 7.
This generator supports this feature by generating the required [JsonDerivedType]
attributes for you.
All missing [JsonDerivedType]
attributes are generated if at least one [JsonDerivedType]
or [JsonPolymorphic]
attribute is specified.
using Funcky;
using System.Text.Serialization;
[DiscriminatedUnion]
[JsonPolymorphic]
public abstract partial record Shape
{
public sealed partial record Rectangle(double Width, double Length) : Shape;
public sealed partial record Circle(double Radius) : Shape;
public sealed partial record EquilateralTriangle(double SideLength) : Shape;
}
Generated code
using System.Text.Serialization;
[JsonDerivedType(typeof(Rectangle), typeDiscriminator: nameof(Rectangle))]
[JsonDerivedType(typeof(Circle), typeDiscriminator: nameof(Circle))]
[JsonDerivedType(typeof(EquilateralTriangle), typeDiscriminator: nameof(EquilateralTriangle))]
partial record Shape
{
// ...
}
Set GeneratePartitionExtension
to true to auto-generate partition methods for IEnumerable<T>
of your type.
using Funcky;
using System.Text.Serialization;
[DiscriminatedUnion(GeneratePartitionExtension = true)]
public abstract partial record Result
{
public sealed partial record Ok() : Result;
public sealed partial record Warning(string Message) : Result;
public sealed partial record Error(string Message) : Result;
}
Usage
var results = new Result[] { new Result.Ok(), /* ... */ }
// N-Tuple extension method:
var (oks, warnings, errors) = results.Partition();
// Extension method with result selector:
var warningAndErrorCount = results.Partition(resultSelector: (_, warnings, errors) => warnings.Count + errors.Count);