Vogen - Value Object Generator

What is the package?

This is a semi-opinionated library which is a Source Generator to generate Value Objects. The main goal is that the Value Objects generated have almost the same speed and memory performance as using primitives.

The Value Objects wrap simple primitives such as int, string, double etc.

To get started, add this package, and add a type such as:

[ValueObject<int>]
public partial struct CustomerId 
{
}

You can now treat CustomerId as you would an int and there is very little performance difference between the two:

var id = CustomerId.From(42);

And your method signatures change from:

void HandleCustomer(int customerId)

to

void HandleCustomer(CustomerId customerId)

The Source Generator generates code for things like creating the object and for performing equality.

Value Objects help combat Primitive Obsession. Primitive Obsession means being obsessed with primitives. It is a Code Smell that degrades the quality of software.

"Primitive Obsession is using primitive data types to represent domain ideas" #

Some examples:

• instead of int age - we'd have Age age. Age might have validation that it couldn't be negative
• instead of string postcode - we'd have Postcode postcode. Postcode might have validation on the format of the text

The opinions are expressed as:

• A Value Object (VO) is constructed via a factory method named From, e.g. Age.From(12)
• A VO is equatable (Age.From(12) == Age.From(12))
• A VO, if validated, is validated with a private static method named Validate that returns a Validation result
• Any validation that is not Validation.Ok results in a ValueObjectValidationException being thrown

Instead of

int customerId = 42;

... we'd have

var customerId = CustomerId.From(42);

CustomerId is declared as:

[ValueObject<int>]
public partial struct CustomerId 
{
}

That's all you need to do to switch from a primitive to a Value Object.

Here it is again with some validation

[ValueObject<int>]
public partial struct CustomerId 
{
    private static Validation Validate(int value) => 
        value > 0 ? Validation.Ok : Validation.Invalid(); 
}

This allows us to have more strongly typed domain objects instead of primitives, which makes the code easier to read and enforces better method signatures, so instead of:

void DoSomething(int customerId, int supplierId, int amount)

we can have:

void DoSomething(CustomerId customerId, SupplierId supplierId, Amount amount)

Now, callers can't mess up the ordering of parameters and accidentally pass us a Supplier ID in place of a Customer ID.

It also means that validation is in just one place. You can't introduce bad objects into your domain, therefore you can assume that in your domain every ValueObject is valid.

Adding the package

Add the package to your application using

dotnet add package Vogen

This adds a <PackageReference> to your project. You can additionally mark the package as PrivateAssets="all" and ExcludeAssets="runtime".

Setting PrivateAssets="all" means any projects referencing this one won't get a reference to the Vogen package. Setting ExcludeAssets="runtime" ensures the Vogen.SharedTypes.dll file is not copied to your build output (it is not required at runtime).

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
  </PropertyGroup>

  <!-- Add the package -->
  <PackageReference Include="Vogen" Version="4.0.0" 
    PrivateAssets="all" ExcludeAssets="runtime" />
  <!-- -->

</Project>

How does it compare to using native types?

Here's the benchmarks comparing a native int to a ValueObject:

There's hardly any speed overhead, and no memory overhead.

The next most common scenario is using a VO to represent a string: