TT.DomainTypes

A record based solution to the primitive type obsession problem

The problem:

We use primitive types like strings and integers everywhere and we occassionally run into issues where the wrong string variable is passed into a function.

public static string GetExistingUserName(string userName)
{
    ...
}

However this could be accidentally used as so:

public static void Main()
{
    string userName = ReadFromPrivateFunction();
    string  favouriteFood = ReadFromOtherPrivateFunction();

    var existingUserName = GetExistingUserName(favouriteFood); //Nothing stops us from doing this
}

However, if we were to use a domain type, we would get a compile type error preventing us from making such a mistake

public record UserName(string Value) : DomainTypeString(Value);

public record Food(string Value) : DomainTypeString(Value);

Now that we have the Domain Types, that are backed by the record reference type, we can now get intellisense and compile errors.

Now our functions become

public static UserName GetExistingUserName(UserName userName)
{
    ...
}

public static void Main()
{
    UserName userName = ReadFromPrivateFunction();
    Food  favouriteFood = ReadFromOtherPrivateFunction();

    var existingUserName = GetExistingUserName(favouriteFood); //Compile time error here because we cannot assign a Food domain type to a UserName domain type
}

We also get the benefit of intellisense which we help us autocomplete or recommend local variables that match the required domain type.