Path: utzoo!utgpu!attcan!uunet!tut.cis.ohio-state.edu!mailrus!cornell!uw-beaver!uw-june!pattis From: pattis@june.cs.washington.edu (Richard Pattis) Newsgroups: comp.lang.misc Subject: Re: VAR vs. IN/OUT Summary: Binary Search Subprograms and Parameter Modes Message-ID: <8997@june.cs.washington.edu> Date: 11 Aug 89 23:50:16 GMT References: <173@enea.se> Organization: U of Washington, Computer Science, Seattle Lines: 24 I published an article in SIGCSE Volume 20, Number 1 (February 1988) that surveyed 40 CS-1/CS-2 books that used Pascal as their language of discourse. Of those books that included a subprogram for binary searching, 50% passed the parameter as non-VAR. Thus, the running times of all these subprograms was really O(N) not O(Log N) for all Pascal compilers I know; in fact, some programs were recursive, which increased their running time to O(N Log N). Similarly, the space requirements we also increased by this amount. In Ada (most compilers I know) parameter transmission is O(1), regardless of the parameter mode. The use of a correct parameter mode is subject to static semantic rules. A student cannot accidentally omit VAR and then find that the actual parameter matching this formal remains unchanged after the subprogram call. Such inconsistent uses of Ada parameter modes are detected and reported by Ada compilers. The equivalent of Pascal's non-VAR mode (which is rarely needed) can be accomplished in Ada by declaring a local object and initializing it to the value of an IN parameter (most useful for nonrecursive traversing of linked data structures). Finally, Modula-3 and Turing each allow a "constant" (I think) parameter mode that matches the semantics of Ada's IN mode. Rich Pattis