1. Single Value Objects as C# structs
Domain-Driven Design bottom-up
Corniel Nobel, , Kiev

2. 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

3. 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

4. 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

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

6. 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

7. 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

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

9. DateTime TimeSpan Guid9
- Single Value Objects as C# structs

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

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

12. Why To use structS To model Single value objects? Bottom-up Approach12
- Single Value Objects as C# structs

13. 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

14. 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

15. 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

16. Example: International Bank Account Number (IBAN)
var iban = IBAN.Parse("nl20ingb "); Console.WriteLine(“Your IBAN: {0:F}", iban); // Your IBAN: NL20 INGB 16
- Single Value Objects as C# structs

17. 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

18. 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

19. 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

20. 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. 21
- Single Value Objects as C# structs

22. “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

23. github.com/Corniel/Qowaiv23
- Single Value Objects as C# structs

24. nuget.org/packages/Qowaiv24
- Single Value Objects as C# structs

25. 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

26. Questions? 26
- Single Value Objects as C# structs

27. Disclaimer
This document contains certain statements and expectations that are forward looking, and which are based on information and plans that are currently available. By their nature, such forward-looking statements and expectations generate risk and uncertainty because they concern factors and events in the future and depend on circumstances that may not occur.
Unforeseen factors that could influence the statements and expectations may, for instance, be changes in expenditures by companies in the markets we operate in; economic, political and foreign exchange fluctuations; possible statutory changes; changes in salary levels of employees; or future takeovers and divestitures.
Exact can therefore not guarantee the accuracy and completeness of such statements and expectations, nor that such statements and expectations will be realized. Actual results may differ materially. Exact refuses to accept any obligation to update statements made in this document.

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