And if you want a more authoritative opinion on that check out what the C++ core guidelines are saying [1]:
> ES.71: Prefer a range-for-statement to a for-statement when there is a choice > Reason > Readability. Error prevention. Efficiency. Best regards Anton [1] https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-for-range сб, 29 сент. 2018 г. в 16:13, Anton Chernov <mecher...@gmail.com>: > +1 > > Maybe it's not necessary to enforce usage of range-based for, but I would > highly encourage to to it due to already named advantages. If code would be > introduced using the old-style there could be a comment suggesting the new > way. But why do the manual work and not leave that to the automated tool? > > And since it's already automated - wouldn't it be better to keep a unified > modern style? > > Just to make this a trend - C++ evolves quickly and this will not be only > upgrade that would needed to be made. And the easier such upgrades get > accepted the easier in general is to upgrade the codebase. > > Soon the standard will get ranges and concepts and this will change the > way C++ applications get written significantly. It is a good habit to be > open for changes and keep up with the trends. By using the new > possibilities the language can offer you prepare yourself for further > changes and are more likely to accept them, evolving your programming style. > > Take a look at a new examples on modern usages (taken from [1]): > > // since C++17 > for (auto&& [first,second] : mymap) { > // use first and second > } > > // since C++20 > for (auto& x : foo().items()) { /* .. */ } // undefined behavior if foo() > returns by value > for (T thing = foo(); auto& x : thing.items()) { /* ... */ } // OK > > // since C++11 > struct cow_string { /* ... */ }; > // a copy-on-write string cow_string str = /* ... */; > // for(auto x : str) { /* ... */ } // may cause deep copy > for(auto x : std::as_const(str)) { /* ... */ } > > Regarding performance: it's really easy to prove that generated assembly > is not changing at all. There is a really handy tool for that [2]. You can > check online the assembly for different language constructs and different > compilers. > > Best regards, > Anton > > [1] https://en.cppreference.com/w/cpp/language/range-for > [2] https://gcc.godbolt.org > > сб, 29 сент. 2018 г. в 13:15, kellen sunderland < > kellen.sunderl...@gmail.com>: > >> It's more readable because it's concise and it's consistent for many types >> you're looping over (i.e. primitive arrays, stl iterators, etc all work >> the >> same way). It's also useful because it's consistent with other >> programming >> languages, making C++ codebases much easier to read for novice and >> intermediate developers. IMO it also leads to better naming in loop >> bodies >> as the concise style means you're less likely to have important 1 letter >> variable names describing loop elements (e.g. no int i =0 or it ...). >> More >> motivation can be found in the cpp standards proposals for C++11 >> http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1868.html and >> http://open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3853.htm. >> >> >> >> On Sat, Sep 29, 2018 at 6:38 PM Naveen Swamy <mnnav...@gmail.com> wrote: >> >> > Kellen, >> > >> > Could you please explain why you think range loops are better and how it >> > improves readability? this is a relatively new feature, many of them >> are >> > used to the old syntax, shouldn't we leave it for the developers to >> choose >> > the one that best suits the need and their familiarity. >> > In general I support the notion of standardizing where necessary, >> enforcing >> > rules on loops seems little bit like micro-managing how you should write >> > C++ code for MXNet. >> > >> > -1(open to change based on new information) >> > >> > >> > >> > On Fri, Sep 28, 2018 at 5:20 PM Chris Olivier <cjolivie...@gmail.com> >> > wrote: >> > >> > > ok then, my vote is still -1, however, because it’s just adding >> needless >> > > friction for developers imho. >> > > >> > > On Fri, Sep 28, 2018 at 7:42 AM kellen sunderland < >> > > kellen.sunderl...@gmail.com> wrote: >> > > >> > > > "Range loops aren’t always the most performant way" Do you have an >> > > example >> > > > where there's a perf difference? >> > > > >> > > > "In addition, sometimes you want the index. Or maybe you want to >> > iterate >> > > > backwards, or not start from the first, etc. Maybe you want the >> > iterator >> > > > because you remove it from the list at the bottom of the loop.... >> Seems >> > > > like a rule for the sake of having a rule." >> > > > >> > > > I should have been more clear about this point. If you're using the >> > > index >> > > > in the loop, doing reverse iteration, or not iterating from >> > start-to-end >> > > > this inspection is smart enough to realize it and will not suggest >> > > > optimizing that type of loop. The loops that would be changes are >> > _only_ >> > > > the loops which are detected as equivalent to range-loops. Examples >> > can >> > > be >> > > > found here: >> > > > >> > > >> > >> https://clang.llvm.org/extra/clang-tidy/checks/modernize-loop-convert.html >> > > > or you can look at what's been changed in the ref PR. I've >> initially >> > set >> > > > our confidence level at 'reasonable' but we could also set to 'safe' >> > > which >> > > > would further reduce the number of loops the check would apply to. >> > > > >> > > > -Kellen >> > > > >> > > > On Fri, Sep 28, 2018 at 3:54 PM Chris Olivier < >> cjolivie...@apache.org> >> > > > wrote: >> > > > >> > > > > -1 >> > > > > >> > > > > Range loops aren’t always the most performant way. In addition, >> > > sometimes >> > > > > you want the index. Or maybe you want to iterate backwards, or not >> > > start >> > > > > from the first, etc. Maybe you want the iterator because you >> remove >> > it >> > > > from >> > > > > the list at the bottom of the loop.... Seems like a rule for the >> sake >> > > of >> > > > > having a rule. >> > > > > >> > > > > On Fri, Sep 28, 2018 at 2:12 AM kellen sunderland < >> > > > > kellen.sunderl...@gmail.com> wrote: >> > > > > >> > > > > > Hello MXNet devs, >> > > > > > >> > > > > > I'd like to discuss uniformly adopting C++11 range loops in the >> > MXNet >> > > > > > project. The benefits I see are: >> > > > > > >> > > > > > * Improved C++ readability (examples below). >> > > > > > * Consistency with other languages. The range-loops are quite >> > > similar >> > > > > to >> > > > > > loops almost all other programming languages. Given we're a >> > project >> > > > that >> > > > > > supports many languages this language consistency could be >> positive >> > > for >> > > > > our >> > > > > > community. >> > > > > > * Consistency within the same project. Currently different >> authors >> > > > have >> > > > > > different loops styles which hurts codebase readability. >> > > > > > * Best available performance. There are often multiple ways to >> > > write >> > > > > > loops in C++ with subtle differences in performance and memory >> > usage >> > > > > > between loop methods. Using range-loops ensures we get the best >> > > > possible >> > > > > > perf using an intuitive loop pattern. >> > > > > > * Slightly lower chance for bugs / OOB accesses when dealing >> with >> > > > > indexing >> > > > > > in an array for example. >> > > > > > >> > > > > > If we decide to enable this uniformly throughout the project we >> can >> > > > > enable >> > > > > > this policy with a simple clang-tidy configuration change. >> There >> > > would >> > > > > be >> > > > > > no need for reviewers to have to manually provide feedback when >> > > someone >> > > > > > uses an older C++ loops style. >> > > > > > >> > > > > > -Kellen >> > > > > > >> > > > > > Reference PR: >> > https://github.com/apache/incubator-mxnet/pull/12356/ >> > > > > > Previous clang-tidy discussion on the list: >> > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > >> https://lists.apache.org/thread.html/b0ae5a9df5dfe0d9074cb2ebe432264db4fa2175b89fa43a5f6e36be@%3Cdev.mxnet.apache.org%3E >> > > > > > >> > > > > > ------------------------- >> > > > > > Examples: >> > > > > > for (auto axis_iter = param.axis.begin() ; axis_iter!= >> > > > param.axis.end(); >> > > > > > ++axis_iter) { >> > > > > > CHECK_LT(*axis_iter, static_cast<int>(ishape.ndim())); >> > > > > > stride_[reverse_index] = ishape[*axis_iter]; >> > > > > > ... >> > > > > > --> >> > > > > > for (int axis : param.axis) { >> > > > > > CHECK_LT(axis, static_cast<int>(ishape.ndim())); >> > > > > > stride_[reverse_index] = ishape[axis]; >> > > > > > ... >> > > > > > -------------------------- >> > > > > > for (size_t i = 0; i < in_array.size(); i++) { >> > > > > > auto &nd = in_array[i]; >> > > > > > pre_temp_buf_.emplace_back(nd.shape(), nd.ctx(), true, >> > > nd.dtype()); >> > > > > > } >> > > > > > --> >> > > > > > for (auto & nd : in_array) { >> > > > > > pre_temp_buf_.emplace_back(nd.shape(), nd.ctx(), true, >> > > nd.dtype()); >> > > > > > } >> > > > > > >> > > > > >> > > > >> > > >> > >> >
