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C++17 fixes #591

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davidlt wants to merge 7 commits into from
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C++17 fixes #591

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b490f2e
Fix check for std::apply (R__HAS_STD_APPLY)
davidlt May 26, 2017
f692ada
Set __cplusplus to 201703L for C++1z (C++17)
davidlt May 26, 2017
35469f4
Don't provide std::__ROOT::apply if R__HAS_STD_APPLY is defined
davidlt May 26, 2017
da6e821
Add missing <functional> header
davidlt May 26, 2017
9fc549c
Fix std::string_view usage if compiled in C++17 mode
davidlt May 26, 2017
be8dddd
Apply git clang-format suggested changes
davidlt May 26, 2017
0276049
Provide null-terminated C strings
davidlt May 26, 2017
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2 changes: 1 addition & 1 deletion cmake/modules/RootConfiguration.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -536,7 +536,7 @@ else()
endif()

CHECK_CXX_SOURCE_COMPILES("#include <tuple>
int main() { std::tuple<int> tup;std::apply(tup, [](int){}); return 0;}" found_stdapply)
int main() { std::apply([](int, int){}, std::make_tuple(1,2)); return 0;}" found_stdapply)
if(found_stdapply)
set(hasstdapply define)
else()
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2 changes: 2 additions & 0 deletions core/base/v7/inc/ROOT/impl_tuple_apply.hxx
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Expand Up @@ -65,6 +65,7 @@ decltype(auto) invoke(F&& f, ArgTypes&&... args) {
}
#endif // ndef R__HAS_STD_INVOKE

#ifndef R__HAS_STD_APPLY
// From http://en.cppreference.com/w/cpp/experimental/apply
namespace detail {
template<class F, class Tuple, std::size_t... I>
Expand All @@ -82,6 +83,7 @@ constexpr decltype(auto) apply(F &&f, Tuple &&t) {
std::make_index_sequence < std::tuple_size <
std::decay_t < Tuple >> {} > {});
}
#endif // ndef R__HAS_STD_APPLY
} // namespace __ROOT
} // namespace std

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1 change: 1 addition & 0 deletions hist/hist/v7/inc/ROOT/THistImpl.hxx
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Expand Up @@ -16,6 +16,7 @@
#define ROOT7_THistImpl

#include <cctype>
#include <functional>
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@Axel-Naumann Axel-Naumann Jun 8, 2017

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Thanks, David!

#include "ROOT/RArrayView.hxx"
#include "ROOT/RTupleApply.hxx"

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6 changes: 4 additions & 2 deletions interpreter/llvm/src/tools/clang/lib/Frontend/InitPreprocessor.cpp
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Expand Up @@ -377,9 +377,11 @@ static void InitializeStandardPredefinedMacros(const TargetInfo &TI,
else if (!LangOpts.GNUMode && LangOpts.Digraphs)
Builder.defineMacro("__STDC_VERSION__", "199409L");
} else {
// FIXME: Use correct value for C++17.
// C++17 [cpp.predefined]p1:
// The name __cplusplus is defined to the value 201703L when compiling a
// C++ translation unit.
if (LangOpts.CPlusPlus1z)
Builder.defineMacro("__cplusplus", "201406L");
Builder.defineMacro("__cplusplus", "201703L");
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@pcanal pcanal May 26, 2017

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Don't we need to match clang value?

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@davidlt davidlt May 26, 2017

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There is no real need. The compiler will not care as it's not using this value. Clang 3.9 which is embedded in ROOT already supported majority of C++17 features. Changing __cplusplus to a proper value does not mean that C++17 is out experimental land. This is basically for people who use __cplusplus to figure out what C++ features they want to use.

// C++1y [cpp.predefined]p1:
// The name __cplusplus is defined to the value 201402L when compiling a
// C++ translation unit.
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2 changes: 1 addition & 1 deletion io/io/v7/inc/ROOT/TFile.hxx
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Expand Up @@ -160,7 +160,7 @@ public:

/// Write an object that is already lifetime managed by this TFileImplBase.
void Write(std::string_view name) {
auto dep = Find(name.to_string());
auto dep = Find(std::string(name.data(), name.size()));
WriteMemoryWithType(name, dep.GetPointer().get(), dep.GetType());
}

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6 changes: 3 additions & 3 deletions io/io/v7/src/TFile.cxx
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Expand Up @@ -97,7 +97,7 @@ class TV6Storage: public ROOT::Experimental::Internal::TFileStorageInterface {
}

void WriteMemoryWithType(std::string_view name, const void* address, TClass* cl) final {
fOldFile->WriteObjectAny(address, cl, name.to_string().c_str());
fOldFile->WriteObjectAny(address, cl, name.data());
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@pcanal pcanal May 26, 2017

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Isn't data() not guaranteed to be null terminated? (which WriteObjectAny requires)?

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@davidlt davidlt May 26, 2017

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You are right. Starting C++11 std::string .data() and .c_str() both provide null-terminated result, but the same does not apply to std::string_view. The example I am looking even shows that one needs to create a temporary string and then call .data().

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@davidlt davidlt May 26, 2017

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Could you point me to the comment in the code which states that it's required? At first look I don't see it explicitly mentioned in TBufferFile::WriteObjectClass or TBufferFile::WriteObjectAny and I didn't see any breakage in CMSSW.

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@davidlt davidlt May 26, 2017

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Ops, it should be TDirectoryFile::WriteObjectAny, but same story. No comments mention that it should be null-terminated. Even provided example is not null-terminated.

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@pcanal pcanal May 26, 2017

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Starting C++11 std::string .data() and .c_str() both provide null-terminated result

I somehow did not catch that. Thanks!

Could you point me to the comment in the code which states that it's required?

Humm ... WriteObjectAny takes a const char* and use it as null terminated string, I am not sure why there would be a 'special' comment in this routine to make that explicit ...

It is clear that std::string_view::data is not appropriate here, as this returns the first characters of the view, which could for example be a sub-part of a larger string.

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@davidlt davidlt May 26, 2017

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Weekend already. I was looking at completely different argument :)

}
};
}
Expand Down Expand Up @@ -144,7 +144,7 @@ OpenV6TFile(std::string_view name, const char* mode,
}
} setCacheDirRAII(opts.fCachedRead);

auto v6storage = std::make_unique<TV6Storage>(name.to_string(), GetV6TFileOpts(mode, opts));
auto v6storage = std::make_unique<TV6Storage>(std::string(name.data(), name.size()), GetV6TFileOpts(mode, opts));

using namespace ROOT::Experimental::Internal;
return std::unique_ptr<TFileStorageInterface>{std::move(v6storage)};
Expand Down Expand Up @@ -191,7 +191,7 @@ std::string ROOT::Experimental::TFile::SetCacheDir(std::string_view path) {
std::lock_guard<std::mutex> lock(GetCacheDirMutex());

std::string ret = ::TFile::GetCacheFileDir();
::TFile::SetCacheFileDir(path.to_string().c_str());
::TFile::SetCacheFileDir(path.data());
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@pcanal pcanal May 26, 2017

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Don't we need a null terminated string here?
Alternatively, what about adding a string_view overload of ::TFile::SetCacheFileDir ?

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@davidlt davidlt May 26, 2017

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Yeah, we could do that.

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@davidlt davidlt May 26, 2017

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At the end I didn't like idea of overload. It would cause more lines to be changed at this point and wouldn't work with TString (ambiguity). Let's do more minimal change for now.

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@pcanal pcanal May 27, 2017

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Actually, we don't need an overload just a replacement as a string_view can be constructed implicitly from a const char*. I uploaded the change in signature of TFile::SetCacheFileDir.

return ret;
}

Expand Down