ProductName.cs

using FPrimitive;

public class ProductName
{
    private readonly string _value;

    /// Prevents a default instance of the type from being created.
    private ProductName(string value)
    {
        _value = value;
    }

    /// Creates a product name instance based on untrusted data.
    public static ValidationResult<ProductName> Create(string untrusted)
    {
        return Spec.Of<string>()
                   .NotNull("Product name should not be 'null'")
                   .NotEmpty("Product name should not be empty")
                   .NotWhiteSpace("Product name should not contain only white-space characters")
                   .Regex("^[a-zA-Z ]+$", "Product name should only contain characters from a-z")
                   .CreateModel(untrusted, validated => new ProductName(validated));
    }
}