Typeflags

Typeflags refer to a compact set of bitwise flags attached to a type in a programming language's metadata or runtime. They encode core characteristics of the type so software components can make fast decisions about how to use it without parsing the full type definition. In practice, a typeflag is a bitfield; each bit represents a property such as whether the type is abstract, sealed, an interface, a class, an enum, or a value type (as opposed to a reference type). Other common flags indicate generics, serializability, visibility (public vs non-public), whether the type has a finalizer, and whether it is nested inside another type. Some environments also flag the presence of a default constructor or whether the type is primitive.

Typeflags are typically stored in the type's metadata description, sometimes as part of a type descriptor or a dedicated TypeAttributes or TypeFlags enumeration. The runtime and reflection APIs read these flags to implement type checks, casting, memory layout decisions, serialization, and interop. They support quick tests such as isAbstract or isSerializable, enabling efficient code paths in the JIT compiler and in libraries that inspect types at runtime.

Examples and naming vary by ecosystem: in .NET, type metadata uses TypeAttributes (a metadata flag set). In other languages, similar flags may be embedded in internal descriptors or enumerations. While the exact flags differ, the general concept remains a concise, binary representation of a type's essential properties.