Standard library header <generator> (C++23)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Standard library headers

Language support
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <stdfloat> (C++23) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11) <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
Concepts
<concepts> (C++20)
Diagnostics
<stdexcept> <stacktrace> (C++23)	<cassert>	<cerrno>	<system_error> (C++11)
Memory management
<memory>	<memory_resource> (C++17)	<scoped_allocator> (C++11)
Metaprogramming
<type_traits> (C++11)	<ratio> (C++11)
General utilities
<utility> <tuple> (C++11) <optional> (C++17) <variant> (C++17)	<any> (C++17) <expected> (C++23) <bitset>	<functional> <typeindex> (C++11) <execution> (C++17)	<charconv> (C++17) <format> (C++20) <bit> (C++20)
Strings
<string_view> (C++17) <string>	<cctype> <cwctype>	<cstring> <cwchar>	<cuchar> (C++11)
Containers
<array> (C++11) <deque> <forward_list> (C++11) <list>	<vector> <map> <set> <unordered_map> (C++11)	<unordered_set> (C++11) <queue> <stack> <flat_map> (C++23)	<flat_set> (C++23) <span> (C++20) <mdspan> (C++23)
Iterators
<iterator>
Ranges
<ranges> (C++20)	<generator> (C++23)
Algorithms
<algorithm>	<numeric>
Numerics
<cfenv> (C++11) <complex>	<random> (C++11) <valarray>	<cmath>	<numbers> (C++20)
Time
<chrono> (C++11)	<ctime>
Localization
<locale>	<clocale>	<codecvt> (C++11/17*)
Input/output
<iosfwd> <iostream> <ios> <streambuf>	<istream> <ostream> <iomanip> <print> (C++23)	<sstream> <spanstream> (C++23) <fstream> <syncstream> (C++20)	<filesystem> (C++17) <cstdio> <cinttypes> (C++11) <strstream> (C++98*)
Regular expressions
<regex> (C++11)
Concurrency support
<stop_token> (C++20) <thread> (C++11) <atomic> (C++11)	<stdatomic.h> (C++23) <mutex> (C++11) <shared_mutex> (C++14)	<condition_variable> (C++11)   <semaphore> (C++20) <latch> (C++20)	<barrier> (C++20) <future> (C++11)
C compatibility
<cstdbool> (C++11/17/20*)   <ccomplex> (C++11/17/20*)	<ctgmath> (C++11/17/20*)	<cstdalign> (C++11/17/20*)	<ciso646> (until C++20)

 

Classes
generator (C++23)	A view that represents synchronous coroutine generator (class template)

Synopsis

namespace std {
  // class template generator
  template<class Ref, class V = void, class Allocator = void>
  class generator;
 
  namespace pmr {
    template<class Ref, class V = void>
    using generator = std::generator<Ref, V, polymorphic_allocator<>>;
  }
}

Class template std::generator

namespace std {
  template<class Ref, class V = void, class Allocator = void>
  class generator : public ranges::view_interface<generator<Ref, V, Allocator>> {
  private:
    using value = conditional_t<is_void_v<V>, 
                                remove_cvref_t< Ref >, V>;          // exposition only
    using reference = conditional_t<is_void_v<V>, Ref&&, Ref>;      // exposition only
 
    // class generator::iterator
    class iterator;                                                 // exposition only
 
  public:
    using yielded =
      conditional_t<is_reference_v<reference>, reference, const reference&>;
 
    // class generator::promise_type
    class promise_type;
 
    generator(const generator&) = delete;
    generator(generator&& other) noexcept;
 
    ~generator();
 
    generator& operator=(generator other) noexcept;
 
    iterator begin();
    default_sentinel_t end() const noexcept;
 
  private:
    coroutine_handle<promise_type> coroutine_ = nullptr;  // exposition only
    unique_ptr<stack<coroutine_handle<>>> active_;        // exposition only
  };
}

Class std::generator::promise_type

namespace std {
  template<class Ref, class V, class Allocator>
  class generator<Ref, V, Allocator>::promise_type {
  public:
    generator get_return_object() noexcept;
 
    suspend_always initial_suspend() const noexcept { return {}; }
    auto final_suspend() noexcept;
 
    suspend_always yield_value(yielded val) noexcept;
 
    auto yield_value(const remove_reference_t<yielded>& lval)
      requires is_rvalue_reference_v<yielded> &&
        constructible_from<remove_cvref_t<yielded>, const remove_reference_t<yielded>&>;
 
    template<class R2, class V2, class Alloc2, class Unused>
      requires same_as<typename generator<T2, V2, Alloc2>::yielded, yielded>
      auto yield_value(ranges::elements_of<generator<T2, V2, Alloc2>&&,
                       Unused> g) noexcept;
 
    template<ranges::input_range R, class Alloc>
      requires convertible_to<ranges::range_reference_t<R>, yielded>
      auto yield_value(ranges::elements_of<R, Alloc> r) noexcept;
 
    void await_transform() = delete;
 
    void return_void() const noexcept {}
    void unhandled_exception();
 
    void* operator new(size_t size)
      requires same_as<Allocator, void> || default_initializable<Allocator>;
 
    template<class Alloc, class... Args>
      requires same_as<Allocator, void> || convertible_to<const Alloc&, Allocator>
      void* operator new(size_t size, allocator_arg_t, const Alloc& alloc,
                         const Args&...);
 
    template<class This, class Alloc, class... Args>
      requires same_as<Allocator, void> || convertible_to<const Alloc&, Allocator>
      void* operator new(size_t size, const This&, allocator_arg_t, const Alloc& alloc,
                         const Args&...);
 
    void operator delete(void* pointer, size_t size) noexcept;
 
  private:
    add_pointer_t<yielded> value_ = nullptr;    // exposition only
    exception_ptr except_;                      // exposition only
  };
}

Class std::generator::iterator

namespace std {
  template<class Ref, class V, class Allocator>
  class generator<Ref, V, Allocator>::iterator {
  public:
    using value_type = value;
    using difference_type = ptrdiff_t;
 
    iterator(iterator&& other) noexcept;
    iterator& operator=(iterator&& other) noexcept;
 
    reference operator*() const noexcept(is_nothrow_copy_constructible_v<reference>);
    iterator& operator++();
    void operator++(int);
 
    friend bool operator==(iterator i, default_sentinel_t);
 
  private:
    coroutine_handle<promise_type> coroutine_; // exposition only
  };
}

References

• C++23 standard (ISO/IEC 14882:2023):

• 26.8.2 Header <generator> synopsis [generator.syn]

• 26.8.3 Class template generator [coro.generator.class]

• 26.8.5 Class generator::promise_type [coro.generator.promise]

• 26.8.6 Class generator::iterator [coro.generator.iterator]