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"- Span For when you want to take an array or a vector." How's this different from taking a pair of iterators? "string_view" After having read all those arti

by roel_v 9y ago

"- Span For when you want to take an array or a vector." How's this different from taking a pair of iterators? "string_view" After having read all those articles about c++17's string_view, I still don't really get the real differences. OK, when parsing (i.e. using many substrings) it makes sense (but then you'd usually work with char* anyway); and maybe some people interact with C libraries that only take char* a lot (and in cases where they have to 'cross the boundary' often). So maybe in text-heavy applications (like I imagine C++ application for the web would be) it makes some sense, but I fail to understand why it's causing this much excitement. "Substitute" There are so many fast formatting libraries already - what does this one offer over those? Because it's generally a trade off between completeness/type safety on the one hand, and speed on the other. I use boost::format which is quite slow in benchmarks, but again I don't do much string processing. "base::Time and base::Duration" In what way are these different from boost::date_time and std::chrono? Here again the documentation (for Abseil) seem to be missing. I mean, I'm all for batteries-included libraries - but this just seems to be a few loosely-related classes slapped together and the only reason it's even on here is because it's from Google. There are dozens of similar libraries languishing on sourceforge and github. Compare it to e.g. POCO - this is not even in the same league.

int_19h 9y ago
> I fail to understand why it's causing this much excitement. C++ guys just like zero-overhead abstractions. The more we can get, the better. Passing std::string around has always been a sore point, and occasionally prompted misguided optimizations (like refcounting copy-on-write in g++).
- roel_v 9y ago
  Well yes, I'm what one would call a 'C++ guy' myself. Don't pass around, pass around const std::string&. What I see left and right is people saying 'you'll never pass a const std::string& any more!'. The way I see it: you'd pass a string_view in the cases where, in the past, you would have had to copy a part out of a string (which is rare, except in parsers), or when dealing with char* API's; what's better about passing a string_view than passing const string& ?
  - int_19h 9y ago
    Nothing. But I would disagree that having to copy a part of a string, or having to pass part of a char buffer that is not a string, is all that rare, even outside of parsers.
humanrebar 9y ago
> After having read all those articles about c++17's string_view, I still don't really get the real differences. `string_view` is a much cleaner parameter type. `char*` and a `size_t` is two parameters. `string` is really a character buffer, accepting a character buffer as input is odd. `string_view` can be trivially constructed from most non-string data structures, including `vector<char>` and `array<char>`. And, now that it's standard, `string_view` is a very lightweight dependency to add to your interface compared to `boost` or hand-rolled alternatives. To that last point, I'm not sure I'd use an abseil `string_view`, at least as an interface type, but I appreciate that they have migration to new standards as a design goal.
duneroadrunner 9y ago
> "- Span For when you want to take an array or a vector." > How's this different from taking a pair of iterators? Safety and (a little) convenience. If your function takes a pair of iterators, there's no way to ensure (at compile-time anyway) that both iterators are even pointing into the same array/vector. Also, spans can ensure, with bounds-checking, that only elements within a specified sub-range can be accessed. Such bounds-enforcement is particularly important in cases like, for example, SaferCPlusPlus' "TRASectionSplitter", which is a data type that allows you to partition an array/vector/whatever into subsections that can each be safely accessed/modified concurrently from different threads. ("TRASectionSplitter" is not yet documented, but for those interested, example code can be found here[1].) [1] shameless plug: https://github.com/duneroadrunner/SaferCPlusPlus/blob/master/msetl_example.cpp#L1903 https://github.com/duneroadrunner/SaferCPlusPlus/blob/master...

by roel_v 9y ago

int_19h 9y ago

> I fail to understand why it's causing this much excitement. C++ guys just like zero-overhead abstractions. The more we can get, the better. Passing std::string around has always been a sore point, and occasionally prompted misguided optimizations (like refcounting copy-on-write in g++).

roel_v 9y ago
Well yes, I'm what one would call a 'C++ guy' myself. Don't pass around, pass around const std::string&. What I see left and right is people saying 'you'll never pass a const std::string& any more!'. The way I see it: you'd pass a string_view in the cases where, in the past, you would have had to copy a part out of a string (which is rare, except in parsers), or when dealing with char* API's; what's better about passing a string_view than passing const string& ?
- int_19h 9y ago
  Nothing. But I would disagree that having to copy a part of a string, or having to pass part of a char buffer that is not a string, is all that rare, even outside of parsers.

humanrebar 9y ago

> After having read all those articles about c++17's string_view, I still don't really get the real differences. `string_view` is a much cleaner parameter type. `char*` and a `size_t` is two parameters. `string` is really a character buffer, accepting a character buffer as input is odd. `string_view` can be trivially constructed from most non-string data structures, including `vector<char>` and `array<char>`. And, now that it's standard, `string_view` is a very lightweight dependency to add to your interface compared to `boost` or hand-rolled alternatives. To that last point, I'm not sure I'd use an abseil `string_view`, at least as an interface type, but I appreciate that they have migration to new standards as a design goal.

duneroadrunner 9y ago

> "- Span For when you want to take an array or a vector." > How's this different from taking a pair of iterators? Safety and (a little) convenience. If your function takes a pair of iterators, there's no way to ensure (at compile-time anyway) that both iterators are even pointing into the same array/vector. Also, spans can ensure, with bounds-checking, that only elements within a specified sub-range can be accessed. Such bounds-enforcement is particularly important in cases like, for example, SaferCPlusPlus' "TRASectionSplitter", which is a data type that allows you to partition an array/vector/whatever into subsections that can each be safely accessed/modified concurrently from different threads. ("TRASectionSplitter" is not yet documented, but for those interested, example code can be found here[1].) [1] shameless plug: https://github.com/duneroadrunner/SaferCPlusPlus/blob/master/msetl_example.cpp#L1903 https://github.com/duneroadrunner/SaferCPlusPlus/blob/master...