From Newsgroup: comp.lang.c++

template<typename T>
struct exc_obj : std::expected<T, std::exception_ptr>
{
using super = std::expected<T, std::exception_ptr>;
template<typename ... Args>
exc_obj( Args &&... args );
};

template<typename T>
template<typename ... Args>
exc_obj<T>::exc_obj( Args &&... args ) :
super( [&]() -> super
{
try
{
return T( std::forward<Args>( args ) ... );
}
catch( ... )
{
return std::unexpected( std::current_exception() );
}
}() )
{
}

Object that encapsulates the given class or exception if needed
in an C++23 std::expected.

--- Synchronet 3.21d-Linux NewsLink 1.2

From Newsgroup: comp.lang.c++

My own std::barrier-variant. Slightly simpler than the original.
And the completion function can return a value.

struct xarrival_token
{
xarrival_token() noexcept = default;
xarrival_token( const xarrival_token &tk ) noexcept = default;
xarrival_token &operator =( const xarrival_token &tk ) noexcept = default;
private:
template<std::invocable Complete>
friend struct xbarrier;
int m_id = -1;
};

template<std::invocable Complete>
struct xbarrier
{
static constexpr bool WithReturn = !std::same_as<std::invoke_result_t<Complete>, void>;
using arrive_result = std::conditional_t<WithReturn, std::optional<std::invoke_result_t<Complete>>, void>;
xbarrier( unsigned initial, Complete &&complete );
xbarrier( const xbarrier & ) = delete;
xbarrier &operator =( const xbarrier & ) = delete;
arrive_result arrive( xarrival_token &tk, bool drop = false );
private:
std::mutex m_mtx;
xcondition_variable m_cv;
unsigned m_initial, m_ctr;
bool m_genFlip;
NO_UNIQUE_ADDRESS Complete m_complete;
};

template<std::invocable Complete>
xbarrier<Complete>::xbarrier( unsigned initial, Complete &&complete ) :
m_initial( initial ),
m_ctr( initial ),
m_complete( std::forward<Complete>( complete ) )
{
if constexpr( requires { (bool)m_complete; } )
assert((bool)m_complete);
}

template<std::invocable Complete>
auto xbarrier<Complete>::arrive( xarrival_token &tk, bool drop ) -> arrive_result
{
using namespace std;
unique_lock lock( m_mtx );
assert(m_ctr <= m_initial);
if( !m_initial )
return (arrive_result)nullopt;
m_initial -= drop;
unsigned newId = --m_ctr;
if( bool gen = m_genFlip; m_ctr )
m_cv.wait( lock, [&] { return m_genFlip != gen; } );
else
{
m_ctr = m_initial;
m_genFlip = !gen;
m_cv.notify_all();
}
if( tk.m_id < 0 )
tk.m_id = newId;
if( !tk.m_id )
return m_complete();
return (arrive_result)nullopt;
}
--- Synchronet 3.21d-Linux NewsLink 1.2