From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=BAYES_00,INVALID_DATE autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 109fba,ef0074ec236ba6e3 X-Google-Attributes: gid109fba,public X-Google-Thread: 108717,ef0074ec236ba6e3 X-Google-Attributes: gid108717,public X-Google-Thread: 1108a1,ef0074ec236ba6e3 X-Google-Attributes: gid1108a1,public X-Google-Thread: 1014db,ef0074ec236ba6e3 X-Google-Attributes: gid1014db,public X-Google-Thread: 103376,b19fa62fdce575f9 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 1994-12-02 11:08:00 PST Newsgroups: comp.lang.ada,comp.lang.c,comp.programming,comp.lang.c++,comp.object Path: bga.com!news.sprintlink.net!howland.reston.ans.net!europa.eng.gtefsd.com!news.mathworks.com!noc.near.net!inmet!spock!stt From: stt@spock.camb.inmet.com (Tucker Taft) Subject: Re: Why don't large companies use Ada? Message-ID: Sender: news@inmet.camb.inmet.com Organization: Intermetrics, Inc. References: <3aa7jo$7j@Starbase.NeoSoft.COM> <3bd06n$kbt@felix.seas.gwu.edu> <1994Nov29.154220.27952@cognos.com> Date: Fri, 2 Dec 1994 17:17:15 GMT Xref: bga.com comp.lang.ada:8192 comp.lang.c:33043 comp.programming:5569 comp.lang.c++:39287 comp.object:9329 Date: 1994-12-02T17:17:15+00:00 List-Id: In article <1994Nov29.154220.27952@cognos.com>, Dave Vernest wrote: >Michael Feldman (mfeldman@seas.gwu.edu) wrote: >: In article , >: Tarjei Jensen wrote: > >: >Since technical merits migth not win the day we should face the realities and >: >use the other successful spinoffs to give Ada a better image. > >: Bingo! And let's keep spreading the stories about where Ada has really >: succeeded. Make sure everyone knows about the software behind all >: those CRT's in the airliner cockpit. And in the air-traffic-control system >: on the ground. And (in France, anyway) in the train system that gets >: you from the airport to the Riviera at 300 km/h. And the Swiss PTT's >: electronic-funds-exchange system. And, and... > >Not sure if I'm violating the c.p charter or not... > >With the use of C++, which supports generics and exception- >handling, is there any reason to code mission-critical systems >in Ada anymore?? Advantages / disadvantages?? Although C++ and Ada 9X have very similar functionality, they have quite different philosophies relative to safety. In Ada 9X, all normal language features are by default safe, using a combination of compile-time and run-time consistency checking; you can circumvent checking if you need to in specific circumstances using explicitly "unchecked" programming features. In C++, largely because of its C heritage, many "normal" language features are by default unsafe (e.g. pointer indirection, array indexing, numeric calculations, casting), but if you work at it, you can create and then restrict yourself to safe abstractions (e.g. safe pointers, checked arrays, overflow-checking arithmetic, checked casts). I realize there are advantages and disadvantages to both the default safe and the default unsafe approaches. When trying to verify a mission critical system, the net advantage seems to go to the default safe approach. In Ada 9X, the places where consistency checks are being circumvented are quite visible, and easily localizable. In C++, one must look at essentially every line of the program to check whether one of the potentially unsafe features of the language is being used in an unsafe way. >Dave S. Tucker Taft stt@inmet.com Intermetrics, Inc.