5 ms·

Not having written Ada, but having seen many HN naysayers saying "Why do we need Rust when Ada can do this" and having tried to come up with a well-researched r

by geofft 5y ago

Not having written Ada, but having seen many HN naysayers saying "Why do we need Rust when Ada can do this" and having tried to come up with a well-researched rebuttal, my sense is that there are three options: 1. Your project is static enough that it doesn't need dynamic memory allocation. The control system for a modern passenger jet is a pretty complex project, but you can allocate an object per engine, an object per flap, a struct per landing gear, an object per pilot display, etc. at design time. Even the navigational computers on these aircraft, which take in unbounded structured data about airports and navigational points, often have hard-coded limits. Quoting https://www.mitre.org/sites/default/files/pdf/12_1324.pdf https://www.mitre.org/sites/default/files/pdf/12_1324.pdf : > one widely used FMC [flight management computer] model ... has issues at airports with over 100 arrival and departure procedures. Some airport examples where 100 arrival and departure procedures are exceeded include Cairo, Amsterdam, Madrid, Paris (Le Bourget, Orly and Charles de Gaulle), Mumbai, New Delhi and Beijing. A FMC service bulletin issued states that the aircraft may lose FMC applications in flight with over 100 procedures and flight plan up-linking. Further, another manufacturer has a FMC model with a limit of 99 total procedures and a limit of 8 waypoints per procedure. A third FMC manufacturer has a model with a limit on the amount of arrivals, departure and approaches as shown below: Early models – limit of 70 departures, 70 arrivals, and 29 approaches at an airport. Later models – limit of 130 departures, 130 arrivals, and 39 approaches at an airport. Counterintutitively, this is culturally acceptable for such "high assurance" applications, but WhatsApp gets confusion from the press when it increases the maximum number of participants in a group chat to the "oddly specific number" of 256 (https://i.redd.it/gk7dicv6hsvy.jpg https://i.redd.it/gk7dicv6hsvy.jpg). 2. You use a third-party GC/refcounting library that calls Unchecked_Deallocation internally. 3. There's a 2018 proposal (linked in another reply) for "ownership types", which specifically references Rust's lifetime model as an inspiration. Or, in other words, if your goal is to write a (say) safe implementation of the DOM that can render real-world web pages while efficiently using memory on a general-purpose computer, Ada is probably the wrong tool for the job. Which is fine! It's a great tool for other jobs.

pyjarrett 5y ago
> if your goal is to write a (say) safe implementation of the DOM that can render real-world web pages while efficiently using memory on a general-purpose computer, Ada is probably the wrong tool for the job. Author here. Ada is actually perfect for the use case you listed. As a C++ programmer focusing on performance, the applicability of Ada to "modern problems" was one of the reasons I was playing around with it. Between customizable "storage pools" (Ada's allocators), the easy of interfacing with C, control of type alignment and layout, compiler intrinsics, built-in concurrency types (protected objects for coordinating access, and tasks for splitting work) and a bunch of other things, I have all the tools I need to do this. It's pretty close to the C++ feature set with the face of Pascal, and C++ programmers should feel comfortable working in Ada after only a few months.
- djur 5y ago
  I don't think C++ was the standard intended here for "right tool for the job", but Rust. The quoted example project is a reference to Servo, if I'm not mistaken.
  - pyjarrett 5y ago
    I figured this was what he was referring to, but C++ is more familiar to a lot of people right now, which is why I couched my answer in those terms. Ada would still a good language to that work in.
joakimds 5y ago
Hi Geofft! Ada developer here. When I read and study the Ada reference manual for the 1995 standard I get the impression that the Ada language designers were not thinking of third-party garbage collection or reference counting as the primary way of achieving memory safety but they were thinking of arena pools/storage pools. When one defines an access-to-object type in the 1995 standard one can specify in which storage pool the allocated object ends up in. The Ada standard does not talk about Stack and heap but talks about Stack and Storage pools. I get the impression that the idea is for an Ada application to get a number of storage pools (with statically determined sizes?) and one can allocate objects inside of these and when one is finished with the objects in a pool one deallocates them all at once by emptying the pool and then one can reuse it again. More efficient and less-error-prone than deallocating each object separately. You are right in point number 2 that the door for garbage collection is open in the Ada standard. No Ada compiler vendor has implemented a GC but you are right about it being considered. The idea for arena pool/storage pool can also been seen in the Ada language (also 1995 standard) by being able to define an access-to-object type locally inside a function/subprogram and at the point of the access-to-object types existence some memory is heap allocated (the size of the allocated memory is specified by the access-to-object type definition) and when the access-to-object type goes out of scope the memory is deallocated (without the use of unchecked_deallocation)... so there should be a forth point on arena/storage pools on your list. And it may be more suited for "a (say) safe implementation of the DOM that can render real-world web pages while efficiently using memory on a general-purpose computer". To use storage pools in Ada I would recommend Deepend (https://sourceforge.net/projects/deepend/ https://sourceforge.net/projects/deepend/). Deepend is a storage pool with subpool capabilities for Ada 2012, Ada 2005, and Ada 95. Memory allocations can be associated with subpools and subpools can be deallocated as a whole which provides a safer alternative than managing deletions of individual objects. It also is likely to be more deterministic and efficient than garbage collection.

by geofft 5y ago

pyjarrett 5y ago

> if your goal is to write a (say) safe implementation of the DOM that can render real-world web pages while efficiently using memory on a general-purpose computer, Ada is probably the wrong tool for the job. Author here. Ada is actually perfect for the use case you listed. As a C++ programmer focusing on performance, the applicability of Ada to "modern problems" was one of the reasons I was playing around with it. Between customizable "storage pools" (Ada's allocators), the easy of interfacing with C, control of type alignment and layout, compiler intrinsics, built-in concurrency types (protected objects for coordinating access, and tasks for splitting work) and a bunch of other things, I have all the tools I need to do this. It's pretty close to the C++ feature set with the face of Pascal, and C++ programmers should feel comfortable working in Ada after only a few months.

djur 5y ago
I don't think C++ was the standard intended here for "right tool for the job", but Rust. The quoted example project is a reference to Servo, if I'm not mistaken.
- pyjarrett 5y ago
  I figured this was what he was referring to, but C++ is more familiar to a lot of people right now, which is why I couched my answer in those terms. Ada would still a good language to that work in.

joakimds 5y ago

Hi Geofft! Ada developer here. When I read and study the Ada reference manual for the 1995 standard I get the impression that the Ada language designers were not thinking of third-party garbage collection or reference counting as the primary way of achieving memory safety but they were thinking of arena pools/storage pools. When one defines an access-to-object type in the 1995 standard one can specify in which storage pool the allocated object ends up in. The Ada standard does not talk about Stack and heap but talks about Stack and Storage pools. I get the impression that the idea is for an Ada application to get a number of storage pools (with statically determined sizes?) and one can allocate objects inside of these and when one is finished with the objects in a pool one deallocates them all at once by emptying the pool and then one can reuse it again. More efficient and less-error-prone than deallocating each object separately. You are right in point number 2 that the door for garbage collection is open in the Ada standard. No Ada compiler vendor has implemented a GC but you are right about it being considered. The idea for arena pool/storage pool can also been seen in the Ada language (also 1995 standard) by being able to define an access-to-object type locally inside a function/subprogram and at the point of the access-to-object types existence some memory is heap allocated (the size of the allocated memory is specified by the access-to-object type definition) and when the access-to-object type goes out of scope the memory is deallocated (without the use of unchecked_deallocation)... so there should be a forth point on arena/storage pools on your list. And it may be more suited for "a (say) safe implementation of the DOM that can render real-world web pages while efficiently using memory on a general-purpose computer". To use storage pools in Ada I would recommend Deepend (https://sourceforge.net/projects/deepend/ https://sourceforge.net/projects/deepend/). Deepend is a storage pool with subpool capabilities for Ada 2012, Ada 2005, and Ada 95. Memory allocations can be associated with subpools and subpools can be deallocated as a whole which provides a safer alternative than managing deletions of individual objects. It also is likely to be more deterministic and efficient than garbage collection.