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[release][proto]: MSVC 19.24.28314 (VS 2019 16.4.0) )won't compile proto's generate.hpp
by Löw, Tobias (STEAG Energy Services GmbH) 05 Dec '19

05 Dec '19

Hi, the latest MSVC version (shipped with VS 2019 16.4.0) doesn't compile boost/proto/generate.hpp since there is an old MSVC-fix, which is no longer needed, and now even produces errors. The "develop" branch of proto contains a fix for that since 2015 (!) but it never made it to the master branch. (https://github.com/boostorg/proto/issues/20) Could some please merge it over to make it into release 1.72 - would be really great! Tobias

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[review][fixed_string] FixedString review starts Nov 25
by Joaquin M López Muñoz 05 Dec '19

05 Dec '19

The Boost formal review of Krystian Stasiowski and Vinnie Falco's FixedString library will take place November 25 - December 4, 2019. This is an early call for you to consider participating in the review. Feedback and constructive criciticism from experts and not-so-experts alike is very much welcome. FixedString being a relatively small and straightforward library, you will find it very easy to familiarize yourself with it and contribute back to the community. FixedString provides a dynamically resizable string of characters with compile-time fixed capacity and contiguous embedded storage in which the characters are placed within the string object itself. Its API closely resembles that of std::string. GitHub repository: https://github.com/18/fixed_string Online docs: https://18.github.io/doc/fixed_string If you feel like reviewing FixedString you can start now prepping --though I'd ask you to refrain from submitting actual reviews till Nov 25. Read the docs, download/fork the code, read/run it, maybe try integrating it into some project of yours, ask questions to the authors, preferrably on Boost or Boost Users mailing lists. The FixedString initiative arose from a very lively discussion within the community: https://lists.boost.org/Archives/boost/2019/09/246943.php , so I sincerely hope this review will be a fruitful, crowded one. Don't let me down! Best regards, Joaquín M López Muñoz Review manager for candidate Boost.FixedString

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Generic Image Library
by Siddhartha Sen 05 Dec '19

05 Dec '19

Being new to this, I have tried looking up the functionalities of GIL. I was thinking of implementing the addition of negative image conversion as well to GIL, incorporating the usage of parallel programming using OpenMP library. Is there any demand for that? I feel that parallel programming will massively improve the computational efficiency of GIL.

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[review][fixed_string] review period extended to Dec 8
by Joaquin M López Muñoz 05 Dec '19

05 Dec '19

After conversation with the review wizards, the review period for candidate Boost.FixedString is extended till Sunday, Dec 8. Hopefully this will allow for some more reviews to come in and for the ongoing discussions to stabilize. So, if you're considering to submit your review, now is the time to reserve some time to do so. Thanks to everybody who has contributed so far, it is a very productive review we're having. Joaquín M López Muñoz Review manager for candidate Boost.FixedString

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Re: [boost] [fixed_string][review] Review of fixed_string
by Peter Dimov 05 Dec '19

05 Dec '19

> - everything should ideally be constexpr. The problem here is that > constexpr requires initializing all elements, and this will heavily > penalize runtime uses of f.ex. fixed_string<512>. On compilers with > __builtin_is_constant_evaluated (gcc 9, clang 9) we should use that; > otherwise, it might be worth it to create a specialization for N < some > suitable upper limit. Wait, I have an idea. template<std::size_t N> struct fixed_string { private: std::size_t size_ = 0; union { char first_ = 0; char data_[ N+1 ]; }; public: fixed_string() = default; }; Now default initialization sets just the first char to zero, as we want, and value initialization initializes all data_ to zero and is constexpr. auto f1() { fixed_string<24> s; return s; } auto f2() { constexpr fixed_string<24> s{}; return s; } https://godbolt.org/z/uhf4S4 I don't know if that's defined behavior or not, but if it isn't, it better be.

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[review][fixed_string]
by Peter Koch Larsen 04 Dec '19

04 Dec '19

Dear boosters Here is my review of fixed_string > - What is your evaluation of the design? I have just completed a similar but much less ambitious design - about 700 LOC in total. The purpose is to replace char string[N] representing string in an ageing code base that is C++98 currently and partly embedded. My design does support a partial compatibility with std::string but that was not the primary goal. The interface compatibility of std::string is a nice feature, but I do not see a reason to attempt to make it a drop-in replacement. The non-compatibility with char[N] is missed by me and probably also some other in the embedded domain. It would be nice if fixed_string<N> had size = N + 1 for char types. > - What is your evaluation of the implementation? Nice and clean. As others have noted, constexpr and noexcept support would be nice. I would also prefer if I could have an option that does not require usage of exceptions, perhaps as a configuration option. Specifically, I would like to be able to control error handling (terminate instead of throw, ability to react to undefined behaviour). Also, I would like to have more forgiving functions that could return the status of failing operations. > - What is your evaluation of the documentation? Nice and clean. > - What is your evaluation of the potential usefulness of the library? If the interface could be extended, It could potentially be useful to many - and to me - if I manage to convince my company to ugrade to C++17. So to summarize: 1) compatibility with char[N]: this requires that the size member is removed. In my source, I still have an O(1) size implemented by having data[N] give the free space in the string. If data[N] == 255, this indicates that the real free size is stored in the elements data[N - 1] and below. There are many ways to encode that length portably. 2) append and assign could have companion functions, that behave in spirit like strncpy/strncat. I have named these function try_append and try_assign. 3) Errorhandling strategy available. > - Did you try to use the library? With what compiler? Did you have > any problems? No, just reading code. > - How much effort did you put into your evaluation? A glance? A quick > reading? In-depth study? About three hours reading and writing this comment. > - Are you knowledgeable about the problem domain? Yes. > > And finally, every review should answer this question: > - Do you think the library should be accepted as a Boost library? The constexpr and noexcept parts should be fixed and compatibility with char[] would be nice. But yes, it should be accepted.

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How to handle NULL string for UTF conversion function
by Alexander Grund 04 Dec '19

04 Dec '19

Hi, in my work on Boost.Nowide I encountered a valid NULL string and am unsure how to handle it. Context: Every wrapper functions is basically implemented like: int fFOO(const char* s){ wstackstring const ws(s); // Converts UTF-8 to wchar-buffer/string return _wfFoo(ws.c_str()); } Similar functions like `std::wstring widen(string-or-const-char-ptr)` are provided which can be used like `return _wfFoo(widen(s).c_str());` in the example above. All was fine, because (IIRC) calling e.g. `fopen(NULL)` is not allowed anyway. However `freopen` DOES allow a NULL for the string. So now I'm left with a couple options and would like some opinions on them: 1. Make (w)stackstring aware of NULL input and if default constructed or with NULL return NULL for c_str(). Makes it easy to use as one could even say `return _wfFoo(wstackstring(s).c_str());` w/o any checks but would be inconsistent with the `widen` functions which convert the passed pointer into a std::(w)string and hence require != NULL 2. Disallow NULL (via assert) for all conversions and require manual checking. Best usage would then probably be to ditch the temporary and do `return _wfFoo(s ? wstackstring(s).c_str() : NULL);` 3. Just like 1. but rename (w)stackstring to e.g. (w)cstring (or ncstring/wcstring, or narrow_cstring/wide_cstring) to highlight that it acts like a C-String (and can be NULL as opposed to empty but never NULL) 4. Ditch stackstring entirely. It was complained about by Zach during the review although defended by the author as "stackstring is barely on-stack buffer optimization - it isn't general string and never intended to be so. It isn't in details because it can actually be useful outside library scope." So this would worsen performance a bit as usual SSO are to small for common filenames. Thanks for reading and any insight is welcome! Alex

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[fixed_string] Gavin's review
by Gavin Lambert 04 Dec '19

04 Dec '19

This is my review of the proposed FixedString library. - Do you think the library should be accepted as a Boost library? Yes, I think it should be ACCEPTED into Boost. Regarding the bikeshedding of the library/class name itself, I prefer "fixed_capacity_string", as the most accurately descriptive name I can either think of myself or that I have read posted by others. I don't think we should be afraid of longer class names, even for vocabulary types. People can always alias them to something shorter to save typing. (Second choice would be "array_string", although that risks misinterpreting as "string_array", which is something entirely different. "stack_string" is another possibility, though might be misleading if contained within another object on the heap.) - What is your evaluation of the design? Overall, looks good. I agree with the motivations for creating such a type in the first place. I would prefer if it didn't reinvent some existing storage concepts already provided by boost::static_vector (and I don't entirely buy the "reduce dependencies" arguments); however there are some other justifications for this that I do consider valid (such as static_vector not being constexpr). As previously noted, I think implementing substr to return a string_view is a mistake; this will cause lifetime problems if someone tries to drop-in replace a std::string in existing code (which was one of the motivating use cases). I'm happy with this being implemented as a new method "subview". (Maybe std::string should do the same thing...) However I still disagree with the choice to also provide "substr" but with a fixed_string return type. Its semantics (with regard to the capacity of the returned string) are still sufficiently different from std::string as to make its usage confusing and poor-performance-prone. With the method omitted, someone attempting a drop-in-replacement will get an error and will need to decide how best to handle it (usually by using subview, but this may require other changes to extend lifetime, which is why spelling subview as "substr" was bad). And if they really want a copy of the substring, they can still do that via subview simply by assigning it to a fixed_string variable -- this would also require them to explicitly choose an appropriate capacity, which I regard as a good thing. For similar reasons to the above, my preference is also to entirely omit operator+ (as in the current design). The consumer can decide how to rewrite things to use operator+= instead. (While there are ways to implement operator+, as has been discussed, all of these come with hefty caveats and I don't think a compromise is sufficiently safe.) - What is your evaluation of the implementation? I did not have time to do more than glance at the implementation. Although I did previously note (thanks to Deniz for calling attention to it) that the unconditional #define BOOST_FIXED_STRING_USE_BOOST in config.hpp is not the correct usage for configuration defines in Boost. I also think that this could make better use of Boost.Config's existing defines -- while a stated goal was to also produce a standalone library, this could be done by using Boost.Config inside of Boost and using a standalone mini-config header with equivalent defines only for the standalone build. I'm also dubious about the division of implementation between three identically-named header files. Unless this is required for avoiding-ugly-docs reasons I think it would be preferable to merge these into a single header -- and perhaps only a single header, where Boost.Config is used. Finally, though, I wonder if perhaps a variation of this type should be implemented which has as storage only the array itself without a separate size member. This might better serve some serialization or I/O scenarios (as a drop-in replacement for a raw char array), although with the caveat that it would probably have to rely on strlen-equivalents and thus could not contain embedded nulls (which is why it should be a separate type, if implemented, as this is a larger departure from std::string). As this would also typically have a smaller capacity than other use cases it could do things like zero-init which might be too expensive for the general-purpose fixed_string, but which can be very helpful for serialization scenarios. - What is your evaluation of the documentation? The documentation is very short, but seems sufficient for the small scope of the class. - What is your evaluation of the potential usefulness of the library? I think it will be extremely useful. I do wonder if an immutable_string type would also be useful (especially for constexpr), but that could be a separate library. - Did you try to use the library? With what compiler? Did you have any problems? I did not try it. - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? A quick reading. Probably a couple of hours in total spread over the entire review period. - Are you knowledgeable about the problem domain? Yes, I frequently work on code where heap allocation is constrained or disallowed. And with strings.

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[review][fixed_string] FixedString review starts today
by Joaquin M López Muñoz 04 Dec '19

04 Dec '19

The Boost formal review of Krystian Stasiowski and Vinnie Falco's FixedString library starts today November 25 and extends up to December 4. Description FixedString provides a dynamically resizable string of characters with compile-time fixed capacity and contiguous embedded storage in which the characters are placed within the string object itself. Its API closely resembles that of std::string. Repo and docs GitHub repository: https://github.com/18/fixed_string Online docs: https://18.github.io/doc/fixed_string Review questions Here are some questions you might want to answer in your review: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With what compiler? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? And finally, every review should answer this question: - Do you think the library should be accepted as a Boost library? I invite you to submit your review, either publicly to the developers or the users lists, or else, if for whatever reason you don't want to go public, directly to me. Thank you for investing your time on reviewing Krystian and Vinnie's work and for contributing to the advancement of Boost. Best regards, Joaquín M López Muñoz Review manager for candidate Boost.FixedString

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Error handling benchmarks: LEAF, Boost Outcome
by Emil Dotchevski 02 Dec '19

02 Dec '19

I wrote a benchmark program for LEAF and Boost Outcome. Here are the results: https://github.com/zajo/leaf/blob/master/benchmark/benchmark.md

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Reminder: Master branch closes for the 1.72.0 release on Wednesday
by Marshall Clow 02 Dec '19

02 Dec '19

See the calendar at https://www.boost.org/development/ -- Marshall P.S. Don't forget the release notes!

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Interest in making template programming imperative?
by Tianjiao Yin 02 Dec '19

02 Dec '19

Hi there, Is there any interest in library that makes template programming imperative. Basically it provides following API VAR(T); // define a variable T SET(T, Type1); // Assign T = Type1 GET(T); // This macro will be expanded to Type1 SET(T, Type2); // Re-assign T = Type2 GET(T); // This macro will be expanded to Type2 The same idea applies to constexpr variable as well. I.e. it's possible to re-define constexpr variable after initialization, though this functionality is not implemented yet. - Github: https://github.com/Mizuchi/tm - Try it online: https://godbolt.org/z/yfQb4K Thanks, Tianjiao

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Fixed String review
by Phil Endecott 02 Dec '19

02 Dec '19

Dear All, Here is my review of the proposed Fixed String library. In summary I think this would be a useful thing to have in Boost, but there are a few issues with the code as it currently stands. This is based on studying the code and docs and the previous mailing list discussions in September; I haven't actually tried to use the library. Firstly regarding the name, I would much prefer static_string for consistency with boost::container::static_vector and with P0843. Note that static_vector was the preferred name in an LEWG poll, according to P0843. It's true that "static" is an ambiguous word that does not really convey what is different about this string, but then neither does "fixed" in my opinion; "fixed capacity" would, but just "fixed" sounds more like "immutable" to me. On the subject of P0843, it it worth reading as it contains some useful links and rationale: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0843r2.html Also a more recent r3 update and reference implementation: https://github.com/gnzlbg/static_vector Here are the features that I think are missing, in no particular order; apologies if some of this does exist but I've missed it: - Much more of it should be constexpr. See P0980R1. That mentions that some of char_traits needs to be constexpr as a prerequisite, but even without that things like size() and empty() can be constexpr. There is also a question of whether all of the elements must be initialised (to 0) by the ctor to be constexpr, which could be costly for a large but sparse container, though it does mean that subsequent push_back()s don't need to store terminators; I don't understand all the issues involved here. (I note a comment in the docs suggesting the lack of constexpr may be temporary.) - In the same vein, more of it should be noexcept - why aren't empty() and size() ? - You can add a specialisation for size 0 that turns it into an empty struct. - You can add a string literal operator"". - You can add std::hash overloads. There are various possibilities for what should happen if the capacity is exceeded, including throwing an exception, asserting, and allowing undefined behaviour. I'm not sure what I would really prefer though I think I'd be more likely to assert() than to throw. See P0843r2 again which discusses this. Regarding your deviations from std::string: operator+ has been omitted because you consider it's not possible to determine a reasonable return type; isn't it just size N+M ? Do you reject that just because it could end up rather large after a sequence of additions? I'd agree if it were N*M but not really for N+M. Have I missed something? You've chosen to return a string_view from substr(). I think that's a bit dangerous; code that does "auto a = s.substr(...)" could end up with a dangling view when s is a fixed string; this makes it more difficult than it should be to migrate from one string type to another, or to write generic code. Regarding the docs, it would be great if the reference could have some highlighting (e.g. bright red?) for the few places where it differs from std::string. My own use for this sort of string has often been to store very large numbers of small strings when total memory usage has been a concern. (A good example would be an textual ID code of some sort, like a postal code or an airport code etc.) For this case, the 8-byte overhead for the size_t length field is a concern; I'd like a static_string<6> to need only 8 bytes total. I suggested changing this to the minimum size needed to store values 0 to N in the previous email discussion, but that hasn't been implemented. My initial thought was that static_string should be implemented on top of boost::container::static_vector<char>. My rationale for that was that static_vector is well-established and doesn't need to be re-implemented, and that a string_facade that adapts a vector<char>-like interface into a string-like interface would be a useful component in its own right. (I've tried to write something like this myself, but it gets tedious very quickly writing out all of those special string methods.) But then I discovered that actually boost::container::static_vector is not implemented as a simple size,data[] pair; apparently it contains pointers to its own storage. So it isn't even trivially- copyable. Now that I know that, I wonder if what we really need is a low-storage-overhead static_vector "done properly" (like the P0843 reference implementation), with a string_facade to make static_string from static_vector<char>. On balance, my view is that this proposal is promising but not quite ready yet. I suggest that the authors should be asked to come back in a few months with a revised version. My preferred design would be an improved static_vector and a string_facade that converts it into a static_string, but if they don't want to do that then simply tidying up the constexpr, noexcept and hash issues would be minimally sufficient. Regards, Phil.

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Re: [boost] [Boost-users] [review][fixed_string] FixedString review starts today
by Peter Dimov 02 Dec '19

02 Dec '19

> This one at least does something: > > http://quick-bench.com/g_-BAIENMHQ1Pi1d136FBdp0idQ > > It still measures nothing though; the string isn't actually written. Finally, this one actually bothers to write the characters: http://quick-bench.com/-FUFkLtQeEa3brMf-y139G3Bbcg Quickbenches aren't very representative.

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Re: [boost] [Boost-users] [review][fixed_string] FixedString review starts today
by Peter Dimov 02 Dec '19

02 Dec '19

> Wait, I forgot to increment the size! > > http://quick-bench.com/sI71NY7OpQ8ft27HpELko8q_4xM > > Not much improvement anyway. This one at least does something: http://quick-bench.com/g_-BAIENMHQ1Pi1d136FBdp0idQ It still measures nothing though; the string isn't actually written.

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Re: [boost] [Boost-users] [review][fixed_string] FixedString review starts today
by Peter Dimov 02 Dec '19

02 Dec '19

> > Zach Laine wrote: > > Ok, I tried this myself on Quickbench: > > > > http://quick-bench.com/WZPNHFBKI-hFxThBYRZVjndtBho > > I tried to fix that to add the null terminator, but as a result both > push_backs were entirely optimized away. > > http://quick-bench.com/DtPR9Yov1TSzUFeYRx0ipVvUYBk Wait, I forgot to increment the size! http://quick-bench.com/sI71NY7OpQ8ft27HpELko8q_4xM Not much improvement anyway.

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Boost 1.69 on Fedora/PPC64LE: tests results
by REIX, Tony 02 Dec '19

02 Dec '19

Hi, I'm testing Boost v1.69 on Fedora 31 / PPC64LE , as explained at: https://www.boost.org/development/running_regression_tests.html And I see many errors: 1 Failed test out of about 11 Run tests: # cd status # ../b2 ... Passed 101532 tests Failed 10368 tests 90.7% of tests completed sucsessefully Passed 1188 tests Failed 15 tests 98.8% of tests completed sucsessefully I do not know what I made wrong. So, since I do not see any Fedora/PPC64LE machine in the BuildFarm: https://www.boost.org/development/tests/master/developer/summary.html I'd like to know where I could find the summary of the official tests of Boost 1.69 on Fedora/PPC64LE. Thanks/Regards, Tony Reix

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Matrix Multiplication
by Siddhartha Sen 01 Dec '19

01 Dec '19

Having gone through quite a few libraries, the ones that intrigued me the most are Boost.Algorithms and Boost.GIL. I had an idea for Boost.GIl in fact. Basically what I wish to propose(please do correct me if it already exist) is a library that will have the functionality to convert a image to a negative one (I found the conversion of colour image to black and white functionality, but not this). Also, the process can be massively sped up by the incorporation of parallel programming paradigms like OpenMP. Do let me know what you guys think about this.

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[fixed_string] Why "fixed" rather than "static"?
by Andrzej Krzemienski 29 Nov '19

29 Nov '19

Hi Everyone, First, I would like to thank Vinnie and Krystian for writing and sharing the library. While this is not a review, I would like to share a thought about the choice of name. Given that we have static_vector, which seems to be doing a similar thing, why was this library called fixed_string rather than static_string? I note that name fixed_string has some potential to mislead the users as it might imply that it is the size that is fixed (like "a string that always stores 2-letter country codes"). I am not saying that the name choice is wrong. I would just want to see the rationale. Regards, &rzej;

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Re: [boost] [Boost-users] [review][fixed_string] FixedString review starts today
by Peter Dimov 29 Nov '19

29 Nov '19

> and yes, you can write code that will be correct if op+= doesn't check. Maybe you can, but I apparently can't. This is what I just wrote: void my_append( fixed_string<512> & s, std::string_view s1, std::string_view s2 ) { if( s.size() + s1.size() + s2.size() > s.max_size() ) throw std::length_error( "" ); s += s1; s += s2; } Is this correct? (Spoiler: no.)

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Re: [boost] [Boost-users] [review][fixed_string] FixedString review starts today
by Peter Dimov 29 Nov '19

29 Nov '19

> https://godbolt.org/z/Z37Pmx > https://godbolt.org/z/CXHRKQ I forgot to maintain a 0 terminator in this sketch; it's even worse with it. .L5: add rax, 1 movzx ecx, BYTE PTR [rdx] cmp rax, 512 ja .L11 add rdx, 1 mov BYTE PTR [rdi+7+rax], cl mov BYTE PTR [rdi+8+rax], 0 mov QWORD PTR [rdi], rax cmp rsi, rdx jne .L5 https://godbolt.org/z/nhYZQY .L3: movzx ecx, BYTE PTR [rdx+rax] mov BYTE PTR [rdi+8+rax], cl add rax, 1 mov BYTE PTR [rdi+8+rax], 0 mov QWORD PTR [rdi], rax cmp r8, rax jne .L3 https://godbolt.org/z/pGJRWs

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Re: [boost] [review][fixed_string] FixedString review starts Nov 25
by Peter Dimov 28 Nov '19

28 Nov '19

> Also, a synopsis section in the documentation might have been nice, to > allow one to see all the declarations in one place. (Admittedly, the main > header does serve that purpose somewhat.) I join the others in noting the pervasive lack of constexpr and noexcept. Even the default constructor isn't either. Can't think of a reason why it would throw. (The lack of constexpr is much easier to explain.) Also, Traits template parameters were wrong in C++98, and they remain wrong today, even though the committee has propagated that mistake into string_view.

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Re: [boost] [Boost-users] [review][fixed_string] FixedString review starts today
by Peter Dimov 28 Nov '19

28 Nov '19

> I would "precondition" `op+=( char const (&)[ M ] )` (and op=) by failing > at compile time when M > N, because the size is known, but in > fixed_string's case, the size isn't known. No I wouldn't. :-) The size isn't known in this case either. It's better to diagnose_if the whole thing.

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[STLInterfaces] only three operations?
by Andrzej Krzemienski 28 Nov '19

28 Nov '19

Hi, While the formal review of STLInterfaces has not yet started, some early feedback may be of help. The idea to implement relational operators from binary operator- for random_access_iterator looks too clever for me. Maybe this deserves a mention in the documentation it is from operator- that the library will generate all relational ops. For non-contiguous random_access_iterators (like in deque) it might be suboptimal to do it this way: a directly provided operator== might be faster than the one synthesized from operator-. Of course, I can provide the 6 relops operators myself, but I could have only 2 if the facade were capable of generating operator!= from operator== (and similar). Could operator!= for random_access_iterator be generated from operator!= ? Regards, &rzej;

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[FixedString] Deniz' review
by Deniz Bahadir 27 Nov '19

27 Nov '19

This is my review of Krystian Stasiowski and Vinnie Falco's FixedString library. The important question and its answer upfront: - Do you think the library should be accepted as a Boost library? I think it should be ACCEPTED into Boost. It is a very small (almost trivial) library and in the beginning I was not sure if it really should go into Boost. However, for me it looks like a useful building-block, so I vote ACCEPT. And if I remember correctly Vinnie said he is already having some other libraries using it which he wanted to propose for Boost later, so there seem to be some real use-cases for it already. Besides, Boost already has some other smaller building-block libraries, so FixedString should be in good company. On a side-note: It would be helpful for the Boost library documentation overview (e.g. https://www.boost.org/doc/libs/1_71_0/) to allow more views/sort-orders for listing available Boost libraries than the views/sort-orders which are already there. (Having "building-blocks" and especially "newer C++ standard features for C++03" or similar "standard compatibility" categories for the Boost libraries comes to mind.) OK, now back to the review. - What is your evaluation of the design? The overall design looks straight forward. `boost::fixed_string`'s API resembles that of `std::string` and only the internal representation differs largely. This looks like the correct design for the aimed purpose of this library (to provide a dynamically resizable string with compile-time fixed capacity.) - What is your evaluation of the implementation? The implementation looks solid and also straight forward. However, I have some remarks to make which you can read further down in this email. - What is your evaluation of the documentation? The documentation is quite small, except for the reference section. This, however, should be fine considering the very simple and small focus which FixedString has. Regarding the "Iterators" section, it was not clear to me on first read for which string type the iterators are invalidated when moving/swapping. I think, `boost::fixed_string` is meant and not `std::string`, but that was not obvious from first read and the wording should probably be improved there to be unambiguous. (Maybe make this clear by speaking of "FixedString" or "fixed_string" instead of just "string".) - What is your evaluation of the potential usefulness of the library? For the use-cases mentioned in the "Motivation" section of the documentation it seems to be useful. All other use-cases I could think of are specializations of the mentioned use-cases. - Did you try to use the library? With what compiler? Did you have any problems? No, I have not tried to use the library. However, I am curious to know if Boost.String_Algorithms can operate on `boost::fixed_string`, too. If not, it would be nice for the code of FixedString and/or Boost.String_Algorithms to be modified in such a way that they can inter-operate with each other. - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? I read the documentation, but the reference section I merely visually scanned through. (I assume, there are no mistakes in it, as they mainly resemble the API of `std::string`.) I looked at the implementation but did not look at all function implementations in all depths. I, however, looked at the CMakeLists.txt file, too, and have some remarks for it (see below). Overall, I probably spent about 1.5 hours for the review, not including the writing of this email. - Are you knowledgeable about the problem domain? Only as far as it gets if you are a general user of `std::string`. I have the following additional remarks: * `boost::to_fixed_string` / `boost::detail::max_digits`: - Is the returned `boost::fixed_string` type of `boost::to_fixed_string` large enough to also hold the (plus) sign of an unsigned integer (if a user might want to append it later)? (Reading the comment and implementation of `boost::detail::max_digits` I assume the answer is yes.) Maybe, make this clear in its reference documentation. * "boost/fixed_string/config.hpp": - At the top of this file we have `#define BOOST_FIXED_STRING_USE_BOOST`, which therefore makes all following conditional definitions always use Boost equivalents of standard library types internally. Is it really desired to have it hard-coded here? Shouldn't the user decide if s/he wants to use Boost compatibility types instead of the ones coming from the standard library? * Filenames - I do not really like, that all files have the same name "fixed_string.hpp". There is the main one in "boost/fixed_string", another one in "boost/fixed_string/detail" and a third one in "boost/fixed_string/impl". I would prefer these files having some (at least slightly) different names. * "CMakeLists.txt": - This CMakeLists.txt file is written in Traditional CMake (old style CMake) although requiring CMake 3.5.1 which knows how to handle Modern CMake. You should consider using Modern CMake instead. - You should leave `CMAKE_CXX_FLAGS` untouched. It is for the user of the library, not for the developer! - Similar, set requirements for a specific minimum required C++ version using the `CXX_STANDARD` property instead of hard-coding it into `CMAKE_CXX_FLAGS`. - You should probably replace usage of `include_directories` with `target_include_directories` on the specific targets. - Similar for `add_definitions` and `link_directories`. - Using `file(GLOB...)` for globbing sources is dangerous and CMake might not always realize that some sources have changed. (see note at: https://cmake.org/cmake/help/latest/command/file.html#glob) - In general, I am not sure if that CMakeLists.txt file should have been part of the review, but I recommend to provide a useful and more modern one if this is going to become a part of Boost, too. Best regards, Deniz

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