#include <coroutine>#include <iostream>#include <optional> template<std::movable T>class Generator{public:struct promise_type{        Generator<T> get_return_object(){return Generator{Handle::from_promise(*this)};}staticstd::suspend_always initial_suspend()noexcept{return{};}staticstd::suspend_always final_suspend()noexcept{return{};}std::suspend_always yield_value(T value)noexcept{            current_value= std::move(value);return{};}// Disallow co_await in generator coroutines.void await_transform()= delete;[[noreturn]]staticvoid unhandled_exception(){throw;} std::optional<T> current_value;}; using Handle= std::coroutine_handle<promise_type>; explicit Generator(const Handle coroutine):        m_coroutine{coroutine}{}     Generator()=default;    ~Generator(){if(m_coroutine)            m_coroutine.destroy();}     Generator(const Generator&)= delete;    Generator& operator=(const Generator&)= delete;     Generator(Generator&& other)noexcept:        m_coroutine{other.m_coroutine}{        other.m_coroutine={};}    Generator& operator=(Generator&& other)noexcept{if(this!=&other){if(m_coroutine)                m_coroutine.destroy();            m_coroutine= other.m_coroutine;            other.m_coroutine={};}return*this;} // Range-based for loop support.class Iter{public:void operator++(){            m_coroutine.resume();}const T& operator*()const{return*m_coroutine.promise().current_value;}bool operator==(std::default_sentinel_t)const{return!m_coroutine|| m_coroutine.done();} explicit Iter(const Handle coroutine):            m_coroutine{coroutine}{} private:        Handle m_coroutine;};     Iter begin(){if(m_coroutine)            m_coroutine.resume();return Iter{m_coroutine};} std::default_sentinel_t end(){return{};} private:    Handle m_coroutine;}; template<std::integral T>Generator<T> range(T first,const T last){while(first< last)        co_yield first++;} int main(){for(constchar i: range(65,91))std::cout<< i<<' ';std::cout<<'\n';}

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z