John R. Bandela, MD Beyond struct: Meta- programming a struct Replacement in C++20Disclaimer This is not an official Google library These opinions are my ownStruct struct person { int id = 1; std::string 1, .name = "John"}; p.id = 2; p.name = "JRB"; std::cout << p.id << " " << p.name; }Limitations of struct u No static reflection u No static generation u No required members u Designated initializers types of the struct (see magic_get) there is no way to get the names u Cannot automatically generate a json serializer/deserializer given a struct.No generation u Cannot create a new struct with names

The Many Faces of Struct Tags Kyle Erf and Sam Helman Why are we here? ● To showcase and explain an underused feature of the language ● To galvanize you to consider struct tags as a potential MongoDB Tools (backups, restoration, monitoring…) Both rely heavily on struct tags for communication and configuration. What is a struct tag? From the official spec “A field declaration may be followed unicode string value attached to a struct field. type Candidate struct { Name string `name` Priorities []string `priorities` } type VocalCandidate struct { Name string `name` Priorities

11Metafunctions • A metafunction is not a function but a class/struct 11Metafunctions • A metafunction is not a function but a class/struct • Metafunctions are not part of the language and have no formal formal language support 11Metafunctions • A metafunction is not a function but a class/struct • Metafunctions are not part of the language and have no formal language support • They exist as an idiomatic of existing language features 11Metafunctions • A metafunction is not a function but a class/struct • Metafunctions are not part of the language and have no formal language support • They exist

pi; bool flag; struct EmptyPoint {}; EmptyPoint ep; struct Point { int x, y; }; Point p; struct ObjWithConstructor { ObjWithConstructor() {} }; ObjWithConstructor o1; struct ObjWithVirtualFunction lifetime starts?18 When lifetime starts?20 Constructors & Destructorshttps://godbolt.org/z/ffzG8hPT8 struct Foo { Foo() { std::cout << "Foo()" << std::endl; } ~Foo() { std::cout << "~Foo()" << std::endl; b; } } 1 2 3 4 5 6 7 8 9 10 11 21 Constructors & Destructorshttps://godbolt.org/z/ffzG8hPT8 struct Foo { Foo() { std::cout << "Foo()" << std::endl; } ~Foo() { std::cout << "~Foo()" << std::endl;

std::array = { , , }; // What now? } 1 2 3 4 5 6 7 8 7struct widget { rect bounding_box(); void place(rect r); }; struct bitmap { std::array data; int width, height; }; What now? 17 } 18 8void vertical_center(auto const& c) { struct widget { 1 rect bounding_box(); 2 void place(rect r); 3 }; 4 5 struct bitmap { 6 std::array data; 7 int width center_bitmaps() { struct bitmap_widget : bitmap { rect bounding_box() { ... } void place(rect r) { ... } struct widget { 1 rect bounding_box(); 2 void place(rect r); 3 }; 4 5 struct bitmap { 6

the type system Back to Basics Brian Ruth (he/him) brian.ruth@garmin.comAn Introduction struct region { int size; }; void init_region(char* backing_buffer, size_t buffer_size ) { if(buffer_size current_region.size) { LOG(“Buffer size too small”); return; } //other init code }An Introduction struct region { int size; }; void init_region(char* backing_buffer, size_t buffer_size ) { if(buffer_size current_region.size) { LOG(“Buffer size too small”); return; } //other init code }An Introduction struct region { int size; }; void init_region(char* backing_buffer, size_t buffer_size ) { if(buffer_size

keywords: break default func interface select case defer go map struct chan else goto package switch const fallthrough if range type continue type and var are used to declare all kinds of code elements in Go programs. chan, interface, map and struct are used as parts in some composite type denotations. break, case, continue, default, else, fallthrough left of :=. These items include qualified identifiers, container elements, pointer dereferences and struct field selectors. Pure assignments have no such limit. About the terminology "assignment" Later

1| break default func interface select 2| case defer go map struct 3| chan else goto package switch 4| const fallthrough if range and var are used to declare all kinds of code elements in Go programs. chan, interface, map and struct are used as parts in some composite type denotations. break, case, continue, default, else, fallthrough left of :=. These items include qualified identifiers, container elements, pointer dereferences and struct field selectors. Pure assignments have no such limit. About the terminology "assignment" Later

1| break default func interface select 2| case defer go map struct 3| chan else goto package switch 4| const fallthrough if range and var are used to declare all kinds of code elements in Go programs. chan, interface, map and struct are used as parts in some composite type denotations. break, case, continue, default, else, fallthrough left of :=. These items include qualified identifiers, container elements, pointer dereferences and struct field selectors. Pure assignments have no such limit. About the terminology "assignment" Later

2024 Define a Template template declaration; declaration can be • class / struct • function • type alias • variable • concept template-parameter is class | typename identifier Programming CppCon 2024 In-class definition Class Template Member Functions template struct A { T f() const { return T{}; } template T g(U u) const { return static_cast(u); Programming CppCon 2024 Out-of-class definition Class Template Member Functions template struct A { T f() const; template T g(U u) const; }; template T A::f() const {