Functional Programming on .NET - The Best of Both Worlds - Isaac Abraham - NDC Oslo 2024

Functional programming fundamentally comes down to two core concepts: expressions (everything returns a value) and immutability (data cannot be changed after creation)

C# is primarily an object-oriented language that has added functional features over time, but will always have mutable state at its heart and isn’t optimized for functional programming

Key functional programming patterns include:

• Pure functions instead of stateful objects
• Immutable data structures
• Expression-based programming over statements
• Separation of data and behavior
• Function composition

While C# has functional features like lambdas, records, and pattern matching, these are primarily syntactic sugar and don’t make the language truly functional

F# provides a more natural functional programming experience on .NET because it was designed as a functional-first language, while still allowing object-oriented programming when needed

Benefits of functional programming include:

• Easier testing due to pure functions
• Fewer bugs from immutability
• Simpler composition of functions
• Better concurrency with no shared mutable state
• More maintainable code through separation of concerns

When doing functional programming in C#, focus on:

• Using static methods over instance methods
• Immutable types and data structures
• Expression-based code where possible
• Keeping mutable state at the edges of the application

Rather than trying to force functional programming in C#, consider F# for a better functional programming experience while still leveraging the .NET ecosystem

The functional approach works particularly well for cloud computing, data processing pipelines, and concurrent programming scenarios

You don’t need to learn advanced concepts like monads or category theory to benefit from functional programming - focus on the fundamentals of expressions and immutability