Nesttypes

Nesttypes is a term used to describe the organization of data types that are defined within the scope of another type. In programming and data modeling, nested types enable hierarchical composition by allowing a type to declare other types as its members. This pattern helps model complex objects that naturally contain structured subobjects.

In most languages, a nested type is scoped within the enclosing type and accessed through its containing type. Some languages treat nested types as members that require an instance of the outer type (inner classes), while others allow static or independent nested types. Nesting can be used for encapsulation, namespace management, and to express close coupling between related concepts.

Examples include Java's inner and static nested classes, C#'s nested classes, and TypeScript modules or namespaces that contain related type aliases and interfaces. In data schemas, nested object definitions enable representing hierarchical data such as a Person with an Address object, or a TreeNode where each node has a list of child nodes of the same type.

Benefits include clearer organization of related types, improved encapsulation, and easier serialization logic when subtypes are tightly bound to their container. Drawbacks include increased coupling, longer type names, potential complexity in traversal or code generation, and issues with versioning or reflection.

Common variants include recursive nesting (a type that contains a field of its own type), generic nested types, and nesting across modules or namespaces. Nested types relate to broader concepts such as composition, aggregation, and hierarchical schema design.