Piotr Padlewski via llvm-dev
2016-Dec-30 11:26 UTC
[llvm-dev] [cfe-dev] Modernizing LLVM Coding Style Guide and enforcing Clang-tidy
2016-12-30 11:34 GMT+01:00 Chandler Carruth <chandlerc at gmail.com>:> On Fri, Dec 30, 2016 at 2:08 AM Piotr Padlewski via cfe-dev < > cfe-dev at lists.llvm.org> wrote: > >> Thanks for very accurate responses. >> - I totally agree what Dave and Chandler said about explicit and implicit >> operations, this is what I meant my first email. >> I believe there are places like >> v.emplace_back(A, B); >> istead of >> v.push_back(make_pair(A, B));b >> That can make code simpler. >> > > Do you have examples? The only ones i can come up with are the ones where > the push_back variant literally can't compile because the type isn't > movable. > > Perhaps it would be useful to break down categories of can happen here... > > Case 1: there is one object already -- this is a *conversion* of a type. > - If the author of the conversion made it *implicit*, then > 'v.push_back(x)' just works. > - If the author of the conversion made it *explicit* I would like to see > the name of the type explicitly: 'v.push_back(T(x))'. > > Case 2a: There is a collection of objects that are being composed into an > aggregate. We don't have any interesting logic in the constructor, it takes > an initializer list. > - This should work with 'v.push_back({a, b, c})' > - If it doesn't today, we can fix the type's constructors so that it does. > - Using 'emplace_back' doesn't help much -- you still need {}s to form the > std::initializer_list in many cases. Pair and tuple are somewhat unusual in > not requiring them. > > This sounds extremely reasonable.> Case 2b: A specific constructor needs to be called with an argument list. > These arguments are not merely being aggregated but are inputs to a > constructor that contains logic. > - This is analogous to a case called out w.r.t. '{...}' syntax in the > coding standards[1] > - Similar to that rule, I would like to see a *call to the constructor* > rather than hiding it behind 'emplace_back' as this is a function with > interesting logic. > - That means i would write T(a, b, c) anyways, and 'v.push_back(T(a, b, > c))' works. > > Calling emplace_back with 0 or multiple arguments is a clear way of saying"this constructor takes multiple arguments". We can do it with initializer list with easy way like: v.emplace_back() == v.push_back({}) v.emplace_back(a, b ,c) == v.push_back({a, b, c}) I personally never liked the initializer syntax because of tricky casees like: vector<string> v{{"abc", "def"}}; Which is equivalent of vector<string> v = {std::string("abc", "def")}; That will call std::string ctor with 2 iterators likely crashing, and putting same string might gives us empty string. In this case programmer probably meant std::vector<std:string> v({"abc", "def"}); or std::vector<std::string> v = {"abc", "def"}; But this case is not possible to mess up with push_back (in the case of vector<vector<string>> or something). At least I hope it is not. So avoiding braces is my personal preference. It is fine for me if we would choose to prefer 'v.push_back({a, b, c})' instead of 'v.emplace_back(a, b, c)', ofc as long as most of the community would prefer first form to the second :) [1]: http://llvm.org/docs/CodingStandards.html#do-not-> use-braced-initializer-lists-to-call-a-constructor > > Case 3: Passing objects of type 'T' through 'push_back' fails to compile > because they cannot be copied or moved. > - You *must* use 'emplace_back' here. No argument (obviously). > > My experience with LLVM code and other codebases is that case 3 should be > extremely rare. The intersection of "types that cannot be moved or copied" > and "types that you put into containers" is typically small. > > > Anyways, I don't disagree with this point with a tiny fix: > >> I think in cases like this we can leave it for judgement of contributor. >> > *or reviewer*. ;] > > I continue to think exceptions can be made in rare cases when folks have > good reasons. But I expect this to be quite rare. =] >Piotr -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161230/5fa9fd77/attachment.html>
Piotr Padlewski via llvm-dev
2017-Jan-09 14:17 UTC
[llvm-dev] [cfe-dev] Modernizing LLVM Coding Style Guide and enforcing Clang-tidy
Are there any other comments about changing style guide? I would like to add points like - prefer "using' instead of "typedef" - use default member initialization struct A { void *ptr = nullptr; }; (instead of doing it in constructor) - use default, override, delete - skip "virtual" with override The last point is to get to consensus with push_back({first, second}) or emplace_back(first ,second); 2016-12-30 12:26 GMT+01:00 Piotr Padlewski <piotr.padlewski at gmail.com>:> > > 2016-12-30 11:34 GMT+01:00 Chandler Carruth <chandlerc at gmail.com>: > >> On Fri, Dec 30, 2016 at 2:08 AM Piotr Padlewski via cfe-dev < >> cfe-dev at lists.llvm.org> wrote: >> >>> Thanks for very accurate responses. >>> - I totally agree what Dave and Chandler said about explicit and >>> implicit operations, this is what I meant my first email. >>> I believe there are places like >>> v.emplace_back(A, B); >>> istead of >>> v.push_back(make_pair(A, B));b >>> That can make code simpler. >>> >> >> Do you have examples? The only ones i can come up with are the ones where >> the push_back variant literally can't compile because the type isn't >> movable. >> >> Perhaps it would be useful to break down categories of can happen here... >> >> Case 1: there is one object already -- this is a *conversion* of a type. >> - If the author of the conversion made it *implicit*, then >> 'v.push_back(x)' just works. >> - If the author of the conversion made it *explicit* I would like to see >> the name of the type explicitly: 'v.push_back(T(x))'. >> >> Case 2a: There is a collection of objects that are being composed into an >> aggregate. We don't have any interesting logic in the constructor, it takes >> an initializer list. >> - This should work with 'v.push_back({a, b, c})' >> - If it doesn't today, we can fix the type's constructors so that it does. >> - Using 'emplace_back' doesn't help much -- you still need {}s to form >> the std::initializer_list in many cases. Pair and tuple are somewhat >> unusual in not requiring them. >> >> This sounds extremely reasonable. > >> Case 2b: A specific constructor needs to be called with an argument list. >> These arguments are not merely being aggregated but are inputs to a >> constructor that contains logic. >> - This is analogous to a case called out w.r.t. '{...}' syntax in the >> coding standards[1] >> - Similar to that rule, I would like to see a *call to the constructor* >> rather than hiding it behind 'emplace_back' as this is a function with >> interesting logic. >> - That means i would write T(a, b, c) anyways, and 'v.push_back(T(a, b, >> c))' works. >> >> Calling emplace_back with 0 or multiple arguments is a clear way of > saying "this constructor takes multiple arguments". > We can do it with initializer list with easy way like: > v.emplace_back() == v.push_back({}) > v.emplace_back(a, b ,c) == v.push_back({a, b, c}) > > I personally never liked the initializer syntax because of tricky casees > like: > > vector<string> v{{"abc", "def"}}; > Which is equivalent of > vector<string> v = {std::string("abc", "def")}; > That will call std::string ctor with 2 iterators likely crashing, and > putting same string might gives us empty string. > > In this case programmer probably meant > std::vector<std:string> v({"abc", "def"}); > or > std::vector<std::string> v = {"abc", "def"}; > > But this case is not possible to mess up with push_back (in the case of > vector<vector<string>> or something). At least I hope it is not. > So avoiding braces is my personal preference. It is fine for me if we > would choose to prefer 'v.push_back({a, b, c})' instead of 'v.emplace_back(a, > b, c)', ofc as long as most of the community would prefer first form to > the second :) > > > [1]: http://llvm.org/docs/CodingStandards.html#do-not-use- >> braced-initializer-lists-to-call-a-constructor >> >> Case 3: Passing objects of type 'T' through 'push_back' fails to compile >> because they cannot be copied or moved. >> - You *must* use 'emplace_back' here. No argument (obviously). >> >> My experience with LLVM code and other codebases is that case 3 should be >> extremely rare. The intersection of "types that cannot be moved or copied" >> and "types that you put into containers" is typically small. >> >> >> Anyways, I don't disagree with this point with a tiny fix: >> >>> I think in cases like this we can leave it for judgement of contributor. >>> >> *or reviewer*. ;] >> >> I continue to think exceptions can be made in rare cases when folks have >> good reasons. But I expect this to be quite rare. =] >> > > Piotr >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20170109/04661858/attachment.html>
Renato Golin via llvm-dev
2017-Jan-09 15:15 UTC
[llvm-dev] [cfe-dev] Modernizing LLVM Coding Style Guide and enforcing Clang-tidy
On 9 January 2017 at 14:17, Piotr Padlewski via cfe-dev <cfe-dev at lists.llvm.org> wrote:> - prefer "using' instead of "typedef" > - use default member initialization > - use default, override, delete > - skip "virtual" with overrideI thought we had all of those already...> The last point is to get to consensus with > > push_back({first, second}) > or > emplace_back(first ,second);I second Chandler's opinion on this. cheers, --renato
David Blaikie via llvm-dev
2017-Jan-09 16:24 UTC
[llvm-dev] [cfe-dev] Modernizing LLVM Coding Style Guide and enforcing Clang-tidy
On Mon, Jan 9, 2017 at 6:17 AM Piotr Padlewski via cfe-dev < cfe-dev at lists.llvm.org> wrote:> Are there any other comments about changing style guide? > I would like to add points like > > - prefer "using' instead of "typedef" > - use default member initialization > struct A { > void *ptr = nullptr; > }; >> (instead of doing it in constructor) > > - use default, override, delete > - skip "virtual" with override > > The last point is to get to consensus with > > push_back({first, second}) > or > emplace_back(first ,second); >It might be a bit noisy, but I'd be inclined to start a separate thread for each of these on llvm-dev with a clear subject line relevant to each one. So they don't get lost and some of them don't get drowned out by the discussion of others, etc.> > 2016-12-30 12:26 GMT+01:00 Piotr Padlewski <piotr.padlewski at gmail.com>: > > > > 2016-12-30 11:34 GMT+01:00 Chandler Carruth <chandlerc at gmail.com>: > > On Fri, Dec 30, 2016 at 2:08 AM Piotr Padlewski via cfe-dev < > cfe-dev at lists.llvm.org> wrote: > > Thanks for very accurate responses. > - I totally agree what Dave and Chandler said about explicit and implicit > operations, this is what I meant my first email. > I believe there are places like > v.emplace_back(A, B); > istead of > v.push_back(make_pair(A, B));b > That can make code simpler. > > > Do you have examples? The only ones i can come up with are the ones where > the push_back variant literally can't compile because the type isn't > movable. > > Perhaps it would be useful to break down categories of can happen here... > > Case 1: there is one object already -- this is a *conversion* of a type. > - If the author of the conversion made it *implicit*, then > 'v.push_back(x)' just works. > - If the author of the conversion made it *explicit* I would like to see > the name of the type explicitly: 'v.push_back(T(x))'. > > Case 2a: There is a collection of objects that are being composed into an > aggregate. We don't have any interesting logic in the constructor, it takes > an initializer list. > - This should work with 'v.push_back({a, b, c})' > - If it doesn't today, we can fix the type's constructors so that it does. > - Using 'emplace_back' doesn't help much -- you still need {}s to form the > std::initializer_list in many cases. Pair and tuple are somewhat unusual in > not requiring them. > > This sounds extremely reasonable. > > Case 2b: A specific constructor needs to be called with an argument list. > These arguments are not merely being aggregated but are inputs to a > constructor that contains logic. > - This is analogous to a case called out w.r.t. '{...}' syntax in the > coding standards[1] > - Similar to that rule, I would like to see a *call to the constructor* > rather than hiding it behind 'emplace_back' as this is a function with > interesting logic. > - That means i would write T(a, b, c) anyways, and 'v.push_back(T(a, b, > c))' works. > > Calling emplace_back with 0 or multiple arguments is a clear way of saying > "this constructor takes multiple arguments". > We can do it with initializer list with easy way like: > v.emplace_back() == v.push_back({}) > v.emplace_back(a, b ,c) == v.push_back({a, b, c}) > > I personally never liked the initializer syntax because of tricky casees > like: > > vector<string> v{{"abc", "def"}}; > Which is equivalent of > vector<string> v = {std::string("abc", "def")}; > That will call std::string ctor with 2 iterators likely crashing, and > putting same string might gives us empty string. > > In this case programmer probably meant > std::vector<std:string> v({"abc", "def"}); > or > std::vector<std::string> v = {"abc", "def"}; > > But this case is not possible to mess up with push_back (in the case of > vector<vector<string>> or something). At least I hope it is not. > So avoiding braces is my personal preference. It is fine for me if we > would choose to prefer 'v.push_back({a, b, c})' instead of 'v.emplace_back(a, > b, c)', ofc as long as most of the community would prefer first form to > the second :) > > > [1]: > http://llvm.org/docs/CodingStandards.html#do-not-use-braced-initializer-lists-to-call-a-constructor > > Case 3: Passing objects of type 'T' through 'push_back' fails to compile > because they cannot be copied or moved. > - You *must* use 'emplace_back' here. No argument (obviously). > > My experience with LLVM code and other codebases is that case 3 should be > extremely rare. The intersection of "types that cannot be moved or copied" > and "types that you put into containers" is typically small. > > > Anyways, I don't disagree with this point with a tiny fix: > > I think in cases like this we can leave it for judgement of contributor. > > *or reviewer*. ;] > > I continue to think exceptions can be made in rare cases when folks have > good reasons. But I expect this to be quite rare. =] > > > Piotr > > > _______________________________________________ > cfe-dev mailing list > cfe-dev at lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20170109/ac0e683d/attachment.html>
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