Add domain behaviour

The generator owns construction, conversion, equality and text. Everything else about the concept is yours, and lives in the same partial declaration.

A factory of your own

[ValueObject<Guid>]
public readonly partial struct CustomerId : IValueObjectValidator<Guid>
{
    public static CustomerId New() => CreateUnchecked(Guid.CreateVersion7());

    public static ValidationResult ValidateValue(in Guid value)
        => value == Guid.Empty
            ? ValidationResult.Required("A customer identifier must not be empty.")
            : ValidationResult.Success;
}

CreateUnchecked skips normalization and validation. It is legitimate here because the application produced the value itself, and never for input that comes from outside — a request, a file, a message.

Properties derived from the value

[ValueObject<string>(MinLength = 15, MaxLength = 34, Pattern = "^[A-Z]{2}[0-9]{2}[A-Z0-9]{11,30}$")]
public readonly partial struct Iban
{
    public string CountryCode => Value[..2];
}

Value is always normalized and valid on an instance that was constructed, so a derived property can rely on the rules: this one needs no length check, because MinLength = 15 has run.

What not to add

• A constructor. The generator owns it, so that no path skips the rules.
• Fields. A value object holds one value; a concept made of several belongs in an ordinary type that holds several value objects.
• Equality members. The generated ones honour the declared Comparison; a hand-written Equals would not.

Next: Test your value objects, which checks the generated and the hand-written parts together.