Immediatetype

Immediatetype is a term used in programming language design and runtime implementation to describe a type whose values are stored directly in the value itself, without requiring a separate heap-allocated object. In practice, immediates are values that fit inside a machine word and can be manipulated without dereferencing a pointer. To distinguish them from heap-allocated values, runtimes commonly use a tagging scheme that marks a value as immediate or as a reference.

Common characteristics include fast access and low allocation overhead. Because immediates do not need allocation or garbage collection, arithmetic and comparisons on these values can be faster and more cache-friendly. They are often used for simple, frequently manipulated data such as booleans, small integers, and single characters, as well as certain enumerations or simple constants.

Implementation typically relies on tagging. A value is stored in a word with certain low-order or high-order bits used as a tag to indicate that the bits encode an immediate value rather than a pointer to a heap object. The runtime then interprets the remaining bits according to the immediatetype’s rules. This approach enables quick type checks and operations but imposes limits on range and representation.

Trade-offs include a finite encoding space for immediates, which may constrain the size of integers or other primitive data unless more sophisticated tagging schemes are used. Some languages provide unboxed or untagged representations in specific contexts (such as in function calls or data structures) to balance immediates with heap-allocated values. Immediates are a foundational concept in VM and compiler optimizations, influencing performance and memory behavior.