F# - hvorfor, hvordan og til hvad? Rune Ibsen Jyske Bank

Transkript

1 F# - hvorfor, hvordan og til hvad? Rune Ibsen Jyske Bank

2 Rune Ibsen Softwareudvikling Seniorkonsulent Mentoring 10 konsulenter

3 F# Programmeringssprog som oversættes til.net Functional-first, OO second Stærkt typet Udviklingsker på GitHub, Don Syme, Microsoft Research Visual Studio, VSCode, Windows, Mac

4 Historien begynder Microservices til musik streaming REST APIer i ASP.NET, C# samtidige brugere 10 services 6 udviklere Ingen testere unit tests Continuous delivery

5 Mål Koden skal kunne videreudvikles i 10 år Koden skal kunne deployes kontinuerligt Koden skal have høj kvalitet

6 Tilfredshed med kode over tid Primitive obsession Null Virtual method calls Exceptions

7 Primitive obsession Primitive Obsession is using primitive data types to represent domain ideas. For example, we use a String to represent a message, an Integer to represent an amount of money, or a Struct/Dictionary/Hash to represent a specific object. - Ward Cunningham

8 private bool CompleteTransaction( int businesstransactionid, int mongodbtransactionid, int sqldbtransactionid, string user) //...;

9 public class TransactionId public int Value get; set;

10 public class TransactionId public TransactionId(int value) this.value = value; public int Value get;

11 public class TransactionId public TransactionId(int value) this.value = value; public int Value get; [Fact] public void ComparisonIsSane() TransactionId id1 = new TransactionId(123); TransactionId id2 = new TransactionId(123); Assert.True(t1.Equals(t2)); //Fails Assert.True(t1 == t2); //Fails Assert.True(t1.Value == t2.value); //Fails

12 public class TransactionId public TransactionId(int value) this.value = value; public int Value get; public override bool Equals(object obj) var other = obj as TransactionId; if (other == null) return false; return this.value == other.value;

13 public class TransactionId public TransactionId(int value) this.value = value; public int Value get; public override bool Equals(object obj) var other = obj as TransactionId; if (other == null) return false; return this.value == other.value; public override int GetHashCode() => this.value.gethashcode(); public static bool operator ==(TransactionId t1, TransactionId t2) => t1.equals(t2); public static bool operator!=(transactionid t1, TransactionId t2) =>!t1.equals(t2);

14 C# is a very nice language it is just that all the defaults are wrong - Don Syme, skaber af F#

15 null I call it my billion-dollar mistake. [...] But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years. - Tony Hoare

16 null null er fraværet af en værdi null fremgår ikke af typesignaturer Hvornår er nullen valid værdi? Nullable<T> er kun for value typer Maybe<T>

17 public struct Maybe<T> private readonly T _value; public Maybe(T value) if(value == null) HasValue = false; _value = default(t); else _value = value; HasValue = true; public static Maybe<T> Empty() => new Maybe<T>(); public bool HasValue get; public T Value => HasValue? _value : throw new Exception("Cannot access Value when Maybe is empty.");

18 Maybe<TransactionId> ParseTransactionId(string s); Transaction GetTransaction(TransactionId id); Maybe<TransactionId> transactionid = ParseTransactionId(s); if (transactionid.hasvalue) Transaction transaction = GetTransaction(transactionId.Value); /* Do stuff with transaction */

19 public static Maybe<R> Map<T, R>( this Func<T, R> mapper) new : Maybe<R>.Empty(); Maybe<Transaction> transaction = ParseTransactionId(s).Map(id => GetTransaction(id));

20 Maybe<TransactionId> ParseTransactionId(string s); Maybe<Transaction> GetTransaction(TransactionId id); Maybe<TransactionId> transactionid = ParseTransactionId(s); if (transactionid.hasvalue) Maybe<Transaction> maybetransaction = GetTransaction(transactionId.Value); if (maybetransaction.hasvalue) Transaction transaction = maybetransaction.value; /* Do stuff with transaction */

21 Maybe<Maybe<Transaction>> transaction = ParseTransactionId(s).Map(id => GetTransaction(id));

22 public static Maybe<R> Bind<T, R>( this Func<T, Maybe<R>> binder) : Maybe<R>.Empty(); Maybe<Transaction> transaction = ParseTransactionId(s).Bind(id => GetTransaction(id));

23 Maybe<Order> order = ParseTransactionId(s).Bind(GetTransaction).Map(transaction => transaction.orderid).bind(getorder);

24 Maybe<Order> order = from id in ParseTransactionId(s) from transaction in GetTransaction(id) from o in GetOrder(transaction.OrderId) select o;

25 Result Exceptions fremgår ikke af typesignaturer Result<TSuccess,TFailure>

26 public struct Result<TSuccess,TFailure> public bool IsSuccessful get; public TSuccess Success => this.issuccessful? _successvalue : throw new Exception("Cannot access Success on failed Result."); public TFailure Failure => this.issuccessful? throw new Exception("Cannot access Failure on successful Result.") : _failurevalue; Implementation details

27 Result<Order, string> order = ParseTransactionId(s).Bind(GetTransaction).Map(transaction => transaction.orderid).bind(getorder); Result<Order, string> order = from id in ParseTransactionId(s) from transaction in GetTransaction(id) from o in GetOrder(transaction.OrderId) select o;

28 Tilfredshed med kode over tid

29

30 Tilfredshed med kode over tid

31 type TransactionId = TransactionId of int

32 type TransactionId = TransactionId of int let t1 = TransactionId(123) let t2 = TransactionId(123) t1 = t2 //true

33 type TransactionId = TransactionId of int type OrderId = OrderId of int type Name = Name of string type CardNumber = CardNumber of string type Amount = Amount of decimal type PaymentMethod = CreditCard of name : Name * number : CardNumber * expiry : DateTime DebitCard of name : Name * number : CardNumber * expiry : DateTime Cash of Amount type CatalogNumber = CatalogNumber of string type ISRC = ISRC of string type LMID = LMID of string type Product = Album of label : string * catalognumber : CatalogNumber Track of ISRC Video of LMID

34 let processpayment(paymentmethod, product) = match product, paymentmethod with Album(label, catalognumber), CreditCard(_) Album(label, catalognumber), DebitCard(_) -> Ok (TransactionId 123) Album(_), Cash(_) -> Error("Cannot pay for an album with cash") Track(isrc), CreditCard(_, number, _) -> Ok (TransactionId 321) Track(isrc), DebitCard(_) -> Ok (TransactionId 789) Track(isrc), Cash(amount) -> Ok (TransactionId 987) Incomplete pattern matches on this expression. For example, the value '(Video(_),_)' may indicate a case not covered by the pattern(s)

35 let processpayment(paymentmethod, product) = match product, paymentmethod with Album(label, catalognumber), CreditCard(_) Album(label, catalognumber), DebitCard(_) -> Ok (TransactionId 123) Album(_), Cash(_) -> Error("Cannot pay for an album with cash") Track(isrc), CreditCard(_, number, _) -> Ok (TransactionId 321) Track(isrc), DebitCard(_) -> Ok (TransactionId 789) Track(isrc), Cash(amount) -> Ok (TransactionId 987) let mycreditcard = CreditCard(Name("Rune Ibsen ), CardNumber(" "), DateTime(1, 1, 2020)) let backinblack = Album("Epic", CatalogNumber(" ")) let result = processpayment(mycreditcard, backinblack) let transactionid = match result with Ok(transactionId) -> transactionid Error(msg) -> failwith msg

36 var mycreditcard = PaymentMethod.NewCreditCard( Name.NewName("Rune Ibsen"), CardNumber.NewCardNumber(" "), new DateTime(1, 1, 2020)); var backinblack = Product.NewAlbum("Epic", CatalogNumber.NewCatalogNumber(" ")); var result = processpayment(mycreditcard, backinblack); if (result.isok) int transactionid = result.resultvalue.item; /* Do stuff */ else throw new Exception(result.ErrorValue);

37 type Maybe<'T> = Some of 'T None val parsetransactionid : string -> Maybe<TransactionId> val gettransaction : TransactionId -> Maybe<Transaction> val getorder : OrderId -> Maybe<Order> let trygetorder (s : string) : Maybe<Order> = maybe let! transactionid = parsetransactionid(s) let! transaction = gettransaction(transactionid) let orderid = transaction.orderid let! order = getorder(orderid) return order

38 type Result<'TSuccess, 'TFailure> = Success of 'TSuccess Failure of 'TFailure val parsetransactionid : string -> Result<TransactionId, string> val gettransaction : TransactionId -> Result<Transaction, string> val getorder : OrderId -> Result<Order, string> let trygetorder (s : string) : Result<Order, string> = result let! transactionid = parsetransactionid(s) let! transaction = gettransaction(transactionid) let orderid = transaction.orderid let! order = getorder(orderid) return order

39 val parsetransactionid : string -> Async<Result<TransactionId, string>> val gettransaction : TransactionId -> Async<Result<Transaction, string>> val getorder : OrderId -> Async<Result<Order, string>> let trygetorder (s : string) : Async<Result<Order, string>> = asyncresult let! transactionid = parsetransactionid(s) let! transaction = gettransaction(transactionid) let orderid = transaction.orderid let! order = getorder(orderid) return order

40 Tilfredshed med kode over tid

41 Kom i gang Glidende overgang fra C# til F# Start med ét F# projekt i en større løsning Kritisk masse af interesserede udviklere Peer review proces

42 Tak for i dag F# kan adopteres gradvist F# er velegnet til modellering F# gør visse gennemgående begreber eksplicitte Gør verden til et bedre sted

43 C# is a very nice language it is just that all the defaults are wrong - Don Syme, skaber af F#