Using STD library for API surface #374
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@jsuereth @lalitb @ThomsonTan - I think I'm kinda done with this, with the following follow-ups that I will send in a separate PR:
The only part that I feel a bit uneasy about is I also owe a spreadsheet with benchmark results. I added the benchmark, btw. But it'd be nice to illustrate the real benefits in a real-world test case. There could be some further optimization applied on API surface, when we know that a collection is one of standard types and when exporter can operate on a standard type, not needing an intermediate |
| #include <type_traits> | ||
| #ifdef HAVE_CPP_STDLIB | ||
| # include "opentelemetry/std/span.h" | ||
| #else |
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Should there be check forHAVE_ABSEIL macro too, and include absl/span.h if set.
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I was unconditionally using either std::span or gsl::span since GSL span implementation is guaranteed to be 100% conformant, whereas absl::Span is not guarnateed to be conformant. I added a brief description to the markdown document.... Basically for now I'd use variant from absl::variant , because there is no other option that would compile with Visual Studio 2015. But not using absl for Span. I can see if we can use that in a separate PR.
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@lalitb - this is described in the markdown doc here:
https://github.com/open-telemetry/opentelemetry-cpp/blob/maxgolov/nostd_stl/docs/building-with-stdlib.md#note-on-gslspan-vs-abslspan
| #include <string> | ||
| #ifdef HAVE_CPP_STDLIB | ||
| # include "opentelemetry/std/string_view.h" | ||
| #else |
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Not yet. I'm not adding full HAVE_ABSEIL support, planning to only use that for absl::variant with Visual Studio 2015. For string_view we only support nostd::string_view and std::string_view. No support for absl::string_view here.
In all other build systems we prefer the following - in the following order, when HAVE_CPP_STDLIB feature is enabled:
- prefer standard
std::classes in C++14, C++17, C++20 - prefer
gsl::spanfor C++11, C++14, C++17. GSL is the only fully conforming implementation.absl::Spanis NOT 100% standards -conforming. I described this in the markdown doc. - prefer
absl::variantfor v2015: technically this is needed only for C++11 on Windows with vs2015. C++17 already hasstd::variant. We should eventually remove MPark variant (nostd::variant). And borrowabsl::variantinstead of MPark variant.
Otherwise our builds will not work with anything that is compiled with vs2015. I kept MPark variant for now. Basically, Abseil is only needed for variant, and absl::variant itself is only needed for vs2015 support. I did foundation work to resolve these issues: #215 #314
I'll add vs2015 in CI in a separate PR. There is no default runner with vs2015 on GitHub. Installing build tools of that may take considerable amount of time in CI. Gotta be creative to sort out how to deploy it the fastest way.
…try-cpp into maxgolov/nostd_stl
…y/opentelemetry-cpp into maxgolov/nostd_stl
maxgolov
added
the
pr:please-merge
…try-cpp into maxgolov/nostd_stl
> Merge [open-telemetry#374](open-telemetry#374) and rebase from master again.
> Merge [open-telemetry#374](open-telemetry#374) and rebase from master again.
I created a separate design doc to explain the logic and what's done in
docs/building-with-stdlib.md@jsuereth