structure clash - flow based solution

[Alf P. Steinbach]

#include "cppx.hpp"
// using std::move; Found via ADL anyway.
using std::wcout;
using cppx::Boxed;
using cppx::n_items;
using cppx::Pipe;
using cppx::String;

#include <functional>
using std::function;

#include <sstream>
using std::wistringstream;

#include <string>
using std::stoi;

#include <thread>
using std::thread;

using Input_func = auto() -> Boxed<String>;
using Output_func = void( Boxed<String> );

auto boxed_line_input()
-> Boxed<String>
{ return cppx::input_line(); }

void boxed_line_output( Boxed<String> const& box )
{ if( not box.is_empty() ) { wcout << box.item() << "\n"; } }

void lines_to_words(
function<Input_func> const& receive_line,
function<Output_func> const& send_word
)
{
for( ;; )
{
Boxed<String> const line = receive_line();
if( line.is_empty() )
{
send_word( Boxed<String>::empty() );
return;
}
else
{
wistringstream stream( line.item() );
String w;
while( stream >> w ) { send_word( Boxed<String>( w ) ); }
}
}
}

void words_to_lines(
int const max_line_length,
function<Input_func> const& receive_word,
function<Output_func> const& send_line
)
{
String line;
for( ;; )
{
Boxed<String> word_box = receive_word();
if( word_box.is_empty() )
{
break;
}
String& word = word_box.item();
int const previous_length = n_items( line );
if( previous_length == 0 )
{
line = move( word );
}
else if( previous_length + 1 + n_items( word ) > max_line_length )
{
send_line( Boxed<String>( move( line ) ) );
line = move( word );
}
else
{
line += L' ';
line += word;
}
}

if( n_items( line ) > 0 )
{
send_line( Boxed<String>( move( line ) ) );
}
send_line( Boxed<String>::empty() );
}

auto main( int, char** args )
-> int
{
int const w = stoi( args[1] );
Pipe<Boxed<String>> pipe;
thread t1(
lines_to_words,
boxed_line_input,
[&]( Boxed<String> s )-> void { pipe.put( move( s ) ); }
);
thread t2(
words_to_lines,
w,
[&]()->Boxed<String> { return pipe.get(); },
boxed_line_output
);
t1.join(); t2.join();
}