nullable

I created an entity "Person" in Doctrine2, and I added to it an Adress entity, which is a value object (embeddable). I want to allow a Person creation, without an Address, so I tag my embedded as "nullable = true". But on the other hand, my Address entity, if it exists, SHOULD contains at least some information (like city, zip code, etc...). So it has "nullable = false" attributes. Address: type: embeddable fields: [...] city: type: string length: 255 nullable: false Person: type: entity table: null embedded: address: class: Address nullable: true It seems that the "nullable = true" of the

For example, if I have the following data class: data class Data( val name: String = "", val number: Long = 0 ) And functions that can return null : fun newName(): String? {} fun newNumber(): Long? {} I know I can use the following to use the value of the functions if they are not null : val newName = newName() val newNumber = newNumber() val data = Data( if (newName != null) newName else "", if (newNumber != null) newNumber else 0 ) But is there a way to just use the default value specified in the constructor of the Data class when the values are null ? I could not find anything in the

Possible Duplicate: Nullable values in C++ What is the best way to represent nullable member in C++? In C#, we can use Nullable<T> type. Such a data type is very much needed as not everything can have meaningful value. It is so important data type that @Jon Skeet has spent one entire chapter, spanned over 27 pages, describing only Nullable<T> in his outstanding book C# in Depth . One simple example can be a Person class 1 , defined as: struct Person { std::string Name; DateTime Birth; DateTime Death; //... }; As a person always have birthdate, so the Birth member of the above class will always

I have this very simple example: class Program { class A { public bool B; } static void Main() { System.Collections.ArrayList list = null; if (list?.Count > 0) { System.Console.WriteLine("Contains elements"); } A a = null; if (a?.B) { System.Console.WriteLine("Is initialized"); } } } The line if (list?.Count > 0) compiles perfectly which means that if list is null , the expression Count > 0 becomes false by default. However, the line if (a?.B) throws a compiler error saying I can't implicitly convert bool? to bool . Why is one different from the other? Heinzi list?.Count > 0 : Here you compare