C# Discriminated Unions (How it Works for Developers)
As a .NET developer working with dynamic PDF generation using IronPDF, you often need to represent and manage a range of specific types—think of different kinds of document data, logging messages, user roles, or export options. This is where the concept of a C# discriminated union comes into play.
While C# doesn’t have native support for discriminated unions in the way F# or Rust does, you can still simulate discriminated unions effectively. In this blog post, we’ll dive into how to define and use a discriminated union type in C#, demonstrate how to apply it with IronPDF for real-world PDF processing, and explore the benefits this pattern provides—especially when paired with pattern matching.
What Are Discriminated Unions in C#?
Discriminated unions, also known as tagged unions or union types, allow a variable to hold one value from a limited set of possible options, where each option is associated with a unique case identifier.
In other languages like F#, you might define them using the union keyword. C# doesn’t provide this feature natively, but developers can use clever combinations of records, classes, and switch expressions to mimic them.
For example:
public abstract record PdfAction;
public record GenerateReport(string ReportName) : PdfAction;
public record LogError(string Message) : PdfAction;
public record ExportToExcel(string FilePath) : PdfAction;
public abstract record PdfAction;
public record GenerateReport(string ReportName) : PdfAction;
public record LogError(string Message) : PdfAction;
public record ExportToExcel(string FilePath) : PdfAction;
Public MustOverride ReadOnly Property PdfAction() As record
public record GenerateReport(String ReportName) : PdfAction
public record LogError(String Message) : PdfAction
public record ExportToExcel(String FilePath) : PdfAction
Each record above represents a single case of the union. The base PdfAction type is the discriminant.
Why Discriminated Unions Matter in IronPDF Workflows
Imagine you're building a PDF report generator using IronPDF, and you need to perform different actions based on a user’s input—maybe generating a PDF, logging an error, or exporting data.
Using discriminated unions in C# lets you represent these option types cleanly, leading to compile time safety, fewer bugs, and clearer logic.
Here’s how you might use it with IronPDF:
void HandlePdfAction(PdfAction action)
{
switch (action)
{
case GenerateReport r:
var pdf = new IronPdf.HtmlToPdf().RenderHtmlAsPdf("<h1>" + r.ReportName + "</h1>");
pdf.SaveAs(r.ReportName + ".pdf");
break;
case LogError e:
Console.WriteLine("Logging Error: " + e.Message);
break;
case ExportToExcel x:
Console.WriteLine("Exporting to Excel at " + x.FilePath);
break;
default:
throw new NotSupportedException("Unknown action");
}
}
void HandlePdfAction(PdfAction action)
{
switch (action)
{
case GenerateReport r:
var pdf = new IronPdf.HtmlToPdf().RenderHtmlAsPdf("<h1>" + r.ReportName + "</h1>");
pdf.SaveAs(r.ReportName + ".pdf");
break;
case LogError e:
Console.WriteLine("Logging Error: " + e.Message);
break;
case ExportToExcel x:
Console.WriteLine("Exporting to Excel at " + x.FilePath);
break;
default:
throw new NotSupportedException("Unknown action");
}
}
Private Sub HandlePdfAction(ByVal action As PdfAction)
Select Case action
'INSTANT VB TODO TASK: The following 'case' pattern variable is not converted by Instant VB:
'ORIGINAL LINE: case GenerateReport r:
Case GenerateReport r
Dim pdf = (New IronPdf.HtmlToPdf()).RenderHtmlAsPdf("<h1>" & r.ReportName & "</h1>")
pdf.SaveAs(r.ReportName & ".pdf")
'INSTANT VB TODO TASK: The following 'case' pattern variable is not converted by Instant VB:
'ORIGINAL LINE: case LogError e:
Case LogError e
Console.WriteLine("Logging Error: " & e.Message)
'INSTANT VB TODO TASK: The following 'case' pattern variable is not converted by Instant VB:
'ORIGINAL LINE: case ExportToExcel x:
Case ExportToExcel x
Console.WriteLine("Exporting to Excel at " & x.FilePath)
Case Else
Throw New NotSupportedException("Unknown action")
End Select
End Sub
This approach keeps your code organized and robust, and makes it easier for developers to understand all possible options in a single location.
Simulating Discriminated Unions in C# – Struct vs. Record vs. Class
Although C# lacks the union keyword, you can simulate discriminated unions using:
- Records: Ideal for immutable data, and supports pattern matching cleanly.
- Classes: More flexible with inheritance and reference semantics.
- Structs: Useful for value types, but less flexible when dealing with reference types or inheritance.
If performance and memory layout are important—for example, in high-throughput PDF logging—you might consider using struct discriminated unions carefully:
public interface IAction { }
public readonly struct SaveAction : IAction
{
public string FileName { get; }
public SaveAction(string fileName) => FileName = fileName;
}
public interface IAction { }
public readonly struct SaveAction : IAction
{
public string FileName { get; }
public SaveAction(string fileName) => FileName = fileName;
}
Public Interface IAction
End Interface
'INSTANT VB WARNING: VB has no equivalent to the C# readonly struct:
'ORIGINAL LINE: public readonly struct SaveAction : IAction
Public Structure SaveAction
Implements IAction
Public ReadOnly Property FileName() As String
Public Sub New(ByVal fileName As String)
Me.FileName = fileName
End Sub
End Structure
Note: You’ll lose some pattern matching benefits with structs, especially when relying on switch expressions.
Benefits of Using Discriminated Unions in C#
There are several key advantages to adopting this software engineering pattern:
- Compile-time safety: You’ll catch missing cases in a switch expression before runtime.
- Clearer logic: It’s easier to write, comment, and reason about actions with named cases.
- Separation of concerns: You decouple behaviors based on data rather than type hierarchies.
- Refactoring ease: Adding or removing cases becomes more straightforward.
When paired with IronPDF, this makes it easier to manage user input, rendering logic, or create dynamic templates with different value pipelines.
When to Use Discriminated Unions with IronPDF
Here are some practical scenarios where this pattern excels:
- PDF Generation Workflows: Different steps in a document lifecycle (generate, save, email).
- Permission Models: Represent different user access levels.
- Logging Systems: Use discriminated union types for log levels (info, error, debug).
- Unit Tests: Define test actions as union types for maintainable logic trees.
- Export Options: Represent output targets like PDF, Excel, Word as union instances.
Example – Handling PDF Actions from UI Events
Let’s say you're capturing UI events and want to route them to IronPDF tasks using discriminated unions:
public abstract record UserAction;
public record GeneratePdf(string HtmlContent, string FileName) : UserAction;
public record ShowMessage(string Text) : UserAction;
public record ExitApplication() : UserAction;
void OnUserEvent(UserAction action)
{
switch (action)
{
case GeneratePdf pdf:
var renderer = new IronPdf.HtmlToPdf();
var document = renderer.RenderHtmlAsPdf(pdf.HtmlContent);
document.SaveAs(pdf.FileName);
break;
case ShowMessage msg:
MessageBox.Show(msg.Text);
break;
case ExitApplication:
Application.Exit();
break;
}
}
public abstract record UserAction;
public record GeneratePdf(string HtmlContent, string FileName) : UserAction;
public record ShowMessage(string Text) : UserAction;
public record ExitApplication() : UserAction;
void OnUserEvent(UserAction action)
{
switch (action)
{
case GeneratePdf pdf:
var renderer = new IronPdf.HtmlToPdf();
var document = renderer.RenderHtmlAsPdf(pdf.HtmlContent);
document.SaveAs(pdf.FileName);
break;
case ShowMessage msg:
MessageBox.Show(msg.Text);
break;
case ExitApplication:
Application.Exit();
break;
}
}
Public MustOverride ReadOnly Property UserAction() As record
public record GeneratePdf(String HtmlContent, String FileName) : UserAction
public record ShowMessage(String Text) : UserAction
public record ExitApplication() : UserAction
'INSTANT VB TODO TASK: Local functions are not converted by Instant VB:
'void OnUserEvent(UserAction action)
'{
' switch (action)
' {
' case GeneratePdf pdf:
' var renderer = New IronPdf.HtmlToPdf();
' var document = renderer.RenderHtmlAsPdf(pdf.HtmlContent);
' document.SaveAs(pdf.FileName);
' break;
' case ShowMessage msg:
' MessageBox.Show(msg.Text);
' break;
' case ExitApplication:
' Application.@Exit();
' break;
' }
'}
This lets you represent events with clear logic and reduces reliance on public object types or overly dynamic handling.
Future Outlook – Will C# Ever Support Native Discriminated Unions?
There’s already been a proposal to add native support for discriminated unions in C#, especially with growing demand for more expressive type systems. While the language hasn’t yet introduced a true union keyword, C# continues to evolve—bringing features like records, pattern matching, and switch expressions closer to full discriminated union functionality.
.NET developers interested in modern, functional-friendly language constructs will want to watch this space closely.
Final Thoughts
Using discriminated unions in C#, even without native support, can significantly improve how you structure and represent logic in IronPDF applications. By leveraging records, switch expressions, and base classes, you’ll make your codebase more readable, maintainable, and resilient to errors—while also unlocking a more declarative and expressive way to handle PDF-related tasks.
If you're a software engineer building modern, flexible .NET applications, this pattern is a must-have in your toolkit.
Try IronPDF Free Today
Ready to take your C# PDF generation to the next level? Download IronPDF and get started with a free trial. Whether you’re generating documents from HTML, logging exports, or automating reports using discriminated unions—IronPDF gives you the power and performance your app deserves.
Frequently Asked Questions
What are discriminated unions in C#?
Discriminated unions in C# are a way of defining a type that can hold a value that can be one of several different, but fixed, types. This allows for more robust type-checking and clearer code.
How can I simulate discriminated unions in C#?
You can simulate discriminated unions in C# by using class hierarchies or structs with pattern matching. These approaches allow you to define different possible types and enforce type safety.
What are the benefits of using discriminated unions?
Discriminated unions provide benefits such as enhanced readability, maintainability, and type safety in your code. They allow you to manage different data types more effectively.
Can Iron Software products help in implementing discriminated unions?
Iron Software products, like IronPDF and IronXL, focus on enhancing data handling and processing capabilities in .NET applications, which can complement the use of discriminated unions by allowing for more flexible data manipulation and presentation.
How do discriminated unions improve code maintainability?
Discriminated unions improve code maintainability by allowing developers to clearly define and handle different possible data types, reducing the risk of errors and making the code easier to understand and update.
Are there any performance considerations when using discriminated unions?
While discriminated unions can add a layer of abstraction, careful implementation ensures minimal performance impact. Using pattern matching and efficient data structures helps maintain performance.
What is pattern matching in the context of discriminated unions?
Pattern matching is a feature in C# that allows you to check a value against a pattern. When used with discriminated unions, it provides a concise and clear way to handle different types encapsulated in the union.
Can discriminated unions be used with IronOCR?
While IronOCR is specifically designed for optical character recognition, its robust data processing features can be used alongside discriminated unions to handle different text data types effectively.
What is the difference between discriminated unions and enums?
Discriminated unions and enums both allow you to define a fixed set of types, but discriminated unions can hold different types of data, while enums are limited to named constants of a single data type.
How does using discriminated unions affect error handling in C#?
Using discriminated unions can enhance error handling by enabling more precise type-checking and pattern matching, which helps in catching potential errors at compile time rather than runtime.