initializer

An initializer is a construct that provides initial values to a variable or to an object at the moment of creation. Initialization occurs as the value is bound to the variable or built into the object's state, and it is distinct from later assignment, which can alter the value after creation.

Variable initialization can be achieved by literals or expressions attached to a declaration, as in int a = 5; or in a dynamically typed language, a = 5.

Object initialization uses a constructor or equivalent mechanism to set up the internal state of a new instance. Many languages also support initializer lists or designated initializers to specify values for multiple fields at once.

Common forms include: C and C++ brace or list initialization, where a scalar can be initialized with a value and aggregates with a braced list; C99 designated initializers allow naming fields. Java and C# use constructors to perform initialization, with C# also supporting object initializers that assign properties at construction time. JavaScript and JSON-inspired languages allow object literals to initialize properties directly. Python initializes objects via __init__, while Go and Rust use composite literals or struct initialization.

Initialization semantics vary by storage duration and language: static storage in C is zero-initialized; automatic variables may be uninitialized unless explicitly initialized; value initialization in C++ initializes to zero or calls a default constructor depending on context.

Understanding the distinction between initialization and assignment helps prevent uninitialized-use errors and clarifies how programs seed their state at creation.

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