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Functional programing in c#

Timetable

Outline

What is functional programming

  • Focus on functions instead of classes that encapsulate logic
    • Splitting data and logic
    • Small reusable functions are way to go
    • We can also do something like higher order functions to enrich existing functions
    • And by functions I mean methods that return value, not void, because values can be chained
  • Expression over statements
    • Expression is something that returns a value (not void)
    • This is good because we can chain functions on values
    • You can even return a function as a value
  • Immutable state
    • State doesn't change, instead its copies are getting passed around
    • This makes reasoning about code much easier, you don't need to find all the place where you mutate code
    • This can be extremely beneficial when building UI like with Blazor
    • Since it's immutable, you can chain calls on it
    • Thread safe-ish

Why functional in c#

  • It's already there
    • And has been since the earliest c# version
    • We show some examples further down
  • You're already using it
    • We will also show some examples further down
  • Not hard at all
    • Since you're already using it you will be familiar with some of the concepts already
    • The key point here is not to dive deep down into mathematical definitions that functional programming is often described with
    • You can use your own names as you will implement new code, to make it more understantable for you and your team
    • Some people say that learning functional first and OOP later made more sense for them
    • Oposite direction seems less intuitive
  • More power
    • You can write more robust and testable code, when you focus on more smaller functions, testing becomes easy and fast
    • You will also find yourself writing more reusable code, and it will be more easy to reuse, since you should split your data (types) and behaviour (functions)
  • Cleaner Code
    • Smaller functions, less boilerplate, more reusable code, what more do you want from cleaner code

LINQ - It's already there & you're using it

  • The whole library has functional design, mostly based on higher order functions
  • You're just saying what you want to be done, instead of how to do it
  • I think we all agree that this library is one of the most powerfull features of the .net ecosystem

Func<> type - It's already there & you're using it

  • Since you're already using LINQ, youre already treating functions as values that can be passed around
  • You're therefore using something called higher order functions, which we will show later

Expressions over statements - It's already there & you're using it

  • For sure you've written at least one ternary operator
  • And with new c# syntax, you might have even encountered pattern matching, which is (tada) an expression

Immutability - It's already there & maybe you're using it

  • Some things are immutable in c# already, like int string and DateTime, others unfortunatelly, are not.
  • Classes/objects are unfortunatelly, mutable
  • But in newer c#, there is more support for immutable types

So what should we do more ?

  • But Tom, if we're already using so much functional concept in c#, what can we do more ?

Use More LINQ

  • It's there and it's very powerfull, rethink if you rewrite your code using LINQ

Start focusing on expressions and chaining

  • You can do better than just ifs and elses, use expressions and split your functions as well
  • Show example and explain

Start writing your own, small HOFs

  • Once again mentioning LINQ, you can learn from it, and write methods similar to it
  • Show example and explain
  • Surprise question

Data is fine, but what if there's none

  • Introducing void
  • Void makes our life miserable when being more functional in c#
  • You cannot chain methods that return void
  • You cannot create void