2020 Template Metaprogramming: Type Traits ## Metafunctions  ## Metafunctions - Traditional functions have zero+ parameters and return a value (or void) void do_something(); int do_something_else(int, char const*); ## Metafunctions - Traditional functions have zero+ parameters and return a value (or void) void do_something(); function is "return" int do_something_else(int, char const*) { return 42; } ## Metafunctions - Traditional functions have zero+ parameters and return a value (or void) void do_something();

result = mult2(11); ## Boost Metaparse - Haskell Create metafunctions with Haskell like syntax. Import and export metafunctions between C++ and the Haskell like environment. typedef meta_hs ::define<_STR("times4 n = f (f n)">::type metafunctions; typedef metafunctions::get<_STR("fib")> fib; typedef metafunctions::get<_STR("times4")> times4; ## Boost

initialization Simplicity for C++ 10 esp. for programmers cppfront: What’s new Types, reflection, metafunctions, … Simplification through generalization Compatibility for C++ Why • What kind • What plan initialization Simplicity for C++ 10 esp. for programmers cppfront: What’s new Types, reflection, metafunctions, … Simplification through generalization Compatibility for C++ Why • What kind • What plan initialization Simplicity for C++ 10 esp. for programmers cppfront: What’s new Types, reflection, metafunctions, … Simplification through generalization Compatibility for C++ Why • What kind • What plan

COMING Maybe for some of you, it's already here in some form. We are going to get a lot of metafunctions building on the following general form: template auto members_of(T) -> type_list ## REFLECTION IS COMING ## We are going to get a lot of metafunctions in the following pattern: template auto for_each_member_recursively(T) ->

of closure types ## P3096 function parameters ## P2996 reflection, splicers, meta::info, metafunctions  P2996 example: may end up with overlapping pieces that don’t fill in the whole picture Suggested aim: P0707 metafunctions, Andrei’s instrumented_vector, reflect+regenerate any type (“identity”) Learn from related experience

property introduces a data member, a getter, and a setter • We’d like to be able to define such metafunctions ## How to Generate a Property // Equivalent hand-written code struct Book { std::string m_author;

functions, check meta function format and register meta function info for _, metaFunc := range metaFunctions { metaFuncValue := reflect.ValueOf(metaFunc) metaFuncID, metaFuncName := getFuncIDAndName(metaFuncValue)

types - Most types are value types - Non-value types (aka mechanisms) are things like traits, metafunctions, etc. Substance Substance Essence Substance Essence Meaning DEFINITION: An object is meaningless

product • reflection operator (prefix ^) • retruns opaque type std::meta::info • consteval metafunctions over meta::info • splicers [ : refl : ] to produce grammatical elements ## enum to string •

static reflection to C++. - Reflection operator ^T that returns the meta information of a type - Metafunctions are functions that take and return meta information: members_of(^T), name_of(^T) - Splice operator