Lazy Initialization

Lazy instantiation delays certain tasks. It typically improves the startup time of a C# application. This has always been possible to implement. But the .NET Framework now offers the Lazy type, which provides this feature.

Lazy initialization (lazy instantiation) of an object means that its creation is deferred until it is first used. (For this topic, the terms lazy initialization and lazy instantiation are synonymous.) Lazy initialization is primarily used to improve performance, avoid wasteful computation, and reduce program memory requirements.

These are the most common scenarios:

• When you have an object that is expensive to create, and the program might not use it. For example, assume that you have in memory a Customer object that has an Orders property that contains a large array of Order objects that, to be initialized, requires a database connection. If the user never asks to display the Orders or use the data in a computation, then there is no reason to use system memory or computing cycles to create it. By using Lazy to declare the Orders object for lazy initialization, you can avoid wasting system resources when the object is not used.

• When you have an object that is expensive to create, and you want to defer its creation until after other expensive operations have been completed. For example, assume that your program loads several object instances when it starts, but only some of them are required immediately. You can improve the startup performance of the program by deferring initialization of the objects that are not required until the required objects have been created.

Although you can write your own code to perform lazy initialization, we recommend that you use Lazy instead. Lazy and its related types also support thread-safety and provide a consistent exception propagation policy.