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Templates & STL

Templates & STL. Stefan Roiser, Lorenzo Moneta CERN PH /SFT. Current Usage. Template types are highly used in HEP Via STL Libraries provided by external parties E.g. Boost Libraries provided by CERN developers E.g. SMatrix , a library for linear algebra Uses expression templates.

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Templates & STL

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  1. Templates & STL Stefan Roiser, Lorenzo Moneta CERN PH/SFT

  2. Current Usage • Template types are highly used in HEP • Via STL • Libraries provided by external parties • E.g. Boost • Libraries provided by CERN developers • E.g. SMatrix, a library for linear algebra • Uses expression templates Templates & STL

  3. Symbols • Problems • Length of symbols • Source code type typedef std::map<std::string, std::pair<int,int> > MyMap; • Mangled symbol (constructor) __ZNSt3mapISsSt4pairIiiESt4lessISsESaIS0_IKSsS1_EEEC1Ev • Demangled symbol std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::pair<int, int>, std::less<std::basic_string<char, std::char_traits<char>, std:: allocator<char> > >, std::allocator<std::pair<std::basic_string<char, std::char_ traits<char>, std::allocator<char> > const, std::pair<int, int> > > >::map() • Number of symbols • Symbols for member functions of class<T> for every instantiation • Results in • Code bloat • Many of these symbols are not even used • Increased library sizes and load time • E.g. literal type names are stored in reflection libraries • Lengthy compiler error messages Generic vector<T*> ? Templates & STL

  4. Concepts • Narrowing template types a la “concepts” ROOT::Math::LorentzVector<CoordSystem<T> > Must provide functions x(), y(), z() float or double • Currently a wrong instantiation produces LorentzVector.h: In member function 'typenameCoordSystem::ScalarLorentzVector<CoordSystem>::x() const [with CoordSystem = Foo]': testMessage.cxx:13: instantiated from here LorentzVector.h:616: error: 'const structFoo' has no member named 'Px' Templates & STL

  5. Other Issues • Thread safety for STL? • E.g. “Intel Threading Building Blocks” • Provides implementations for hash_map, queue, vector • Enhancements for iterator programming • Simplifications for the coding itself • E.g. using lambda functions Templates & STL

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