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If an object has a property that is a collection, should the object create the collection object or make a consumer check for null? I know the consumer should not assume, just wondering if most people create the collection object if it is never added to.
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In object initializer, you can initialize the value to the fields or properties of a class at the time of creating an object without calling a constructor. In this syntax, you can create an object and then this syntax initializes the freshly created object with its properties, to the variable in the assignment.
Collection initializers let you specify one or more element initializers when you initialize a collection type that implements IEnumerable and has Add with the appropriate signature as an instance method or an extension method. The element initializers can be a simple value, an expression, or an object initializer.
An object initializer is an expression that describes the initialization of an Object . Objects consist of properties, which are used to describe an object. The values of object properties can either contain primitive data types or other objects.
There are two ways to initialize a class object: Using a parenthesized expression list. The compiler calls the constructor of the class using this list as the constructor's argument list. Using a single initialization value and the = operator.
You can also use the "Lazy initailizer" pattern where the collection is not initialized until (and unless) someone accesses the property getter for it... This avoids the overhead of creating it in those cases where the parent object is instantiated for some other purpose that does not require the collection...
public class Division
{
private int divId;
public int DivisionId { get; set; }
private Collection<Employee> emps;
public Collection<Employee> Employees
{ get {return emps?? (emps = new Collection<Employee>(DivisionId));}}
}
EDIT: This implementation pattern is, in general, not thread safe... emps could be read by two different threads as null before first thread finishes modifying it. In this case, it probably does not matter as DivisionId is immutable and although both threads would get different collections, they would both be valid. Whne the second thread fihishes, therefore, emps would be a valid collection. The 'probably' is because it might be possible for the first thread to start using emps before the second thread resets it. That would not be thread-safe. Another slightly more complex implementation from Jon SKeet is thread-safe (see This article on SIngletons for his example/discussion on how to fix this.
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