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C++ 17 Features

1. Language
  • Making the text message for static_assert optional[10]
  • Allow typename (as an alternative to class) in a template template parameter[11]
  • New rules for auto deduction from braced-init-list[12][7]
  • Nested namespace definitions, e.g., namespace X::Y { … } instead of namespace X { namespace Y { … } }[7][13]
  • Allowing attributes for namespaces and enumerators[14][15]
  • New standard attributes [[fallthrough]], [[maybe_unused]] and [[nodiscard]][16]
  • UTF-8 (u8) character literals[14][17] (UTF-8 string literals have existed since C++11; C++17 adds the corresponding character literals for consistency, though as they are restricted to a single byte they can only store ASCII)
  • Hexadecimal floating-point literals[18][19]
  • Constant evaluation for all non-type template arguments[14][20]
  • Fold expressions, for variadic templates[14][21]
  • A compile-time static if with the form if constexpr(expression)[22]
  • Structured binding declarations, allowing auto [a, b] = getTwoReturnValues();[23]
  • Initializers in if and switch statements[24]
  • copy-initialization and direct-initialization of objects of type T from prvalue expressions of type T (ignoring top-level cv-qualifiers) shall result in no copy or move constructors from the prvalue expression. See copy elision for more information.
  • Some extensions on over-aligned memory allocation[25]
  • Class template argument deduction (CTAD), introducing constructor deduction guides, eg. allowing std::pair(5.0, false) instead of requiring explicit constructor arguments types std::pair<double, bool>(5.0, false) or an additional helper template function std::make_pair(5.0, false).[26][27]
  • Inline variables, which allows the definition of variables in header files without violating the one definition rule. The rules are effectively the same as inline functions
  • __has_include, allowing the availability of a header to be checked by preprocessor directives[28]
  • Value of __cplusplus changed to 201703L[29]
  • Exception specifications were made part of the function type[30]
2. Library
  • Most of Library Fundamentals TS I, including:[31][32]
  • std::string_view, a read-only non-owning reference to a character sequence or string-slice[33]
  • std::optional, for representing optional objects, a data type that may not always be returned by a given algorithm with support for non-return
  • std::any, for holding single values of any type
  • std::uncaught_exceptions, as a replacement of std::uncaught_exception in exception handling[34][14]
  • New insertion functions try_emplace and insert_or_assign for std::map and std::unordered_map key-value associative data structures[35][36]
  • Uniform container access: std::size, std::empty and std::data[36][37]
  • Definition of “contiguous iterators”[36][38]
  • A file system library based on boost::filesystem[39]
  • Parallel versions of STL algorithms[40]
  • Additional mathematical special functions, including elliptic integrals and Bessel functions[41]
  • std::variant, a tagged union container[42]
  • std::byte, allowing char to be replaced for data types intending to model a byte of data as a byte rather than a character[43]
  • Logical operator traits: std::conjunction, std::disjunction and std::negation[44]

https://github.com/AnthonyCalandra/modern-cpp-features