ReferenceType

ReferenceType is a category of data types whose values are references to objects stored on the heap, rather than the objects themselves being stored directly in the variable. Variables of a reference type hold addresses that locate the object, while the actual data resides in memory managed separately from the reference.

In practice, assigning a reference type value copies the reference, not the object. This means multiple variables can reference the same object, and changes made through one reference are visible through others. A reference type variable can usually be set to null to indicate the absence of an object, and dereferencing a null reference typically results in a runtime error in most languages.

Memory management for reference types is commonly handled by a garbage collector or runtime allocator. Objects created on the heap remain reachable as long as at least one reference exists; when no references remain, the object becomes eligible for garbage collection. This contrasts with value types, which store their data directly and are copied by value upon assignment.

Language-specific notes: many programming languages treat non-primitive types as reference types. In Java, for example, all non-primitive types (objects, arrays) are reference types. In C#, classes, interfaces, delegates, and arrays are reference types, while structs and primitive numeric types are value types; strings are reference types but are often treated as immutable. The concept helps explain behavior around copying, mutation, nullability, and lifetime management across languages.

See also: value type, garbage collection, null safety, object references.