Single Value Objects as C# structs Domain-Driven Design bottom-up Corniel Nobel, 2016-11-21, Kiev

About me Corniel Nobel Senior Software engineer Exact mail@corniel.nl corniel.nl/blog github.com/Corniel linkedin.com - Single Value Objects as C# structs

Take away What you should know after this talk What a Single Value Object is Benefits of using Single Value Objects Difference between value types and reference types Benefits of modeling Single Value Objects as structs How to code a Single Value Object yourself 3 - Single Value Objects as C# structs

Single Value Object A Value Object Single Value Object A Value Object* that can be represented by a single scalar 4 - Single Value Objects as C# structs

Value Object Equal by value By definition (Domain-Driven Design) Immutable 5 - Single Value Objects as C# structs

Single Value Object Equal by value By definition (Domain-Driven Design) Immutable Subset of primitive type (scalar) Per definition Self-descriptive Not dependent on other data Ubiquitous naming (language) 6 - Single Value Objects as C# structs

The benefits of Single Value Objects Richer contracts/interfaces More descriptive Potential valid by default Centralized (business) logic Serialization Binding Parsing & Formatting Domain specific logic/transformations 7 - Single Value Objects as C# structs

But you already knew that… 8 - Single Value Objects as C# structs

DateTime TimeSpan Guid 9 - Single Value Objects as C# structs

Example: Rich Contract public class President { public string Name { get; set; } public string Email { get; set; } public DateTime DateOfBirth { get; set; } public string CountryOfBirth { get; set; } public int YearOfElection { get; set; } } 10 - Single Value Objects as C# structs

Example: Rich Contract public class President { public string Name { get; set; } public EmailAddress Email { get; set; } public Date DateOfBirth { get; set; } public Country CountryOfBirth { get; set; } public Year YearOfElection { get; set; } } 11 - Single Value Objects as C# structs

Why To use structS To model Single value objects? Bottom-up Approach 12 - Single Value Objects as C# structs

Reference Type (Class) vs. Value Type (Struct) Pointer to data elsewhere in memory Mutable by default Inheritable by default Equal by reference Examples Object String* Type[] Value Type Stores own data (or point to data) Immutable by design* Sealed by design Equal by value Examples Floating points Integers Boolean, Char 13 - Single Value Objects as C# structs

Reference Type (Class) vs. Value Type (Struct) Pointer to data elsewhere in memory Mutable by default Inheritable by default Equal by reference Examples Object String* Type[] Value Type Stores own data (or point to data) Immutable by design* Sealed by design Equal by value Examples Floating Points Integers Boolean, Char 14 - Single Value Objects as C# structs

What do Single Value Objects look like in practice Examples What do Single Value Objects look like in practice 15 - Single Value Objects as C# structs

Example: International Bank Account Number (IBAN) var iban = IBAN.Parse("nl20ingb0001234567"); Console.WriteLine(“Your IBAN: {0:F}", iban); // Your IBAN: NL20 INGB 0001 2345 67 16 - Single Value Objects as C# structs

Example: Postal Code var code = PostalCode.Parse(“H0H0H0"); if (code.IsValid(Country.CA)){ /* ... */ } Console.WriteLine(“Formatted postal code: {0:CA}", code); // Formatted postal code: H0H 0H0 17 - Single Value Objects as C# structs

Example: Stream Size if (file.Length > size){ .. } // Comparable var size = StreamSize.FromMegaBytes(12.4); // Factory method var size = StreamSize.Parse("13 kb"); // Factory method var size = StreamSize.GB; // Constant StreamSize size = 1400; // (Implicit) cast Console.WriteLine("The file was {0:0.0 F}.", size); // The file was 13.0 Kilobyte 18 - Single Value Objects as C# structs

Structs and how they work in .NET var number = default(int); // What is the value of number? var text = default(string); // What is the value of text? public virtual bool Equals(obj other) { // if type and all underlying values are equal return true } public virtual string ToString() { return GetType().ToString(); public virtual int GetHashCode() { return RuntimeHelpers.GetHashCode(this); 19 - Single Value Objects as C# structs

Some design decisions How to (de)serialize (XML, JSON, Memory) Implement IComparable or not Implement IFormattable or not To cast (and which types) or not The scalar to use for the unified internal representation Debug experience 20 - Single Value Objects as C# structs

21 - Single Value Objects as C# structs

“Qowaiv is a (Single) Value Object library “Qowaiv is a (Single) Value Object library. It aims to model reusable (Single) Value Objects that can be used a wide variety of modeling scenarios, both inside and outside a Domain-driven context.” 22 - Single Value Objects as C# structs

github.com/Corniel/Qowaiv 23 - Single Value Objects as C# structs

nuget.org/packages/Qowaiv 24 - Single Value Objects as C# structs

Take away What you should know after this talk What a Single Value Object is Benefits of using Single Value Objects Difference between value types and reference types Benefits of modeling Single Value Objects as structs How to code a Single Value Object yourself 25 - Single Value Objects as C# structs

Questions? 26 - Single Value Objects as C# structs

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