computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...

, a quaject is an

object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ai ...

-like

data structure In computer science, a data structure is a data organization, management, and storage format that is usually chosen for efficient access to data. More precisely, a data structure is a collection of data values, the relationships among them, a ...

containing both data and code (or pointers to code), exposed as an interface in the form of '' callentries'', and can accept a list of callentries to other quajects for '' callbacks'' and '' callouts''. They were developed by

Alexia Massalin Alexia Massalin (formerly Henry Massalin) is an American computer scientist and programmer. She pioneered the concept of superoptimization, and designed the ''Synthesis kernel'', a small kernel with a Unix compatibility layer that makes heavy ...

in 1989 for the ''

Synthesis kernel In computer science, self-modifying code (SMC) is code that alters its own instructions while it is executing – usually to reduce the instruction path length and improve performance or simply to reduce otherwise repetitively similar code, th ...

'', and named for the ''Qua! Machine'', a unique hardware platform built by Massalin. The origin of the term 'qua' is unclear; Massalin claims humorously that it is a sound made by

koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the womb ...

s. The main purpose of quajects is to provide an

abstraction Abstraction in its main sense is a conceptual process wherein general rules and concepts are derived from the usage and classification of specific examples, literal ("real" or "concrete") signifiers, first principles, or other methods. "An abstr ...

to manage

self-modifying code In computer science, self-modifying code (SMC) is code that alters its own instructions while it is executing – usually to reduce the instruction path length and improve performance or simply to reduce otherwise repetitively similar code, ...

, by allowing runtime code optimizing on a per-object basis. While the original Synthesis kernel required quajects to be written in hand-developed

assembly language In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence be ...

, this was done to avoid developing a complex compiler; Massalin noted that

just-in-time compilation In computing, just-in-time (JIT) compilation (also dynamic translation or run-time compilations) is a way of executing computer code that involves compilation during execution of a program (at run time) rather than before execution. This may cons ...

(JIT) for a

high-level programming language In computer science, a high-level programming language is a programming language with strong Abstraction (computer science), abstraction from the details of the computer. In contrast to low-level programming languages, it may use natural language ...

that permits runtime code generation, as in

Lisp A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech. Types * A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lisping ...

Smalltalk Smalltalk is an object-oriented, dynamically typed reflective programming language. It was designed and created in part for educational use, specifically for constructionist learning, at the Learning Research Group (LRG) of Xerox PARC by Alan Ka ...

, can also apply this approach, though she also asserted that the complexity of such a compiler was likely to be prohibitive. Quajects differ from more conventional objects in two key ways: first, they always use a form of the dependency injection pattern to manage both interfaces to other quajects, and continuations out of the quaject; the list of callentry references for this is part of quaject creation, and may be updated during the quaject's lifetime. Second, and more critically, a given quaject's set of methods can be unique to the specific quaject; methods for a type or class of quajects are stored as one or more templates, rather than as fixed code. While shared methods can be accessed through a common table of pointers, individual quajects can also have methods that are generated specifically to tailor the performance for that quaject's behavior.

References

Operating system technology {{comp-sci-stub