console.cpp
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// Copyright 2021 Peter Dimov
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt
#if defined(_MSC_VER)
# pragma warning(disable: 4702) // unreachable code
#endif
#include <boost/describe.hpp>
#include <boost/mp11.hpp>
#include <boost/json.hpp>
#include <boost/utility/string_view.hpp>
#include <string>
#include <stdexcept>
#include <vector>
#include <map>
#include <iostream>
// get variable
template<class Scope> boost::json::value get( Scope& scope, boost::string_view name )
{
using Md = boost::describe::describe_members<Scope, boost::describe::mod_public>;
bool found = false;
boost::json::value result;
boost::mp11::mp_for_each<Md>([&](auto D) {
if( !found && name == D.name )
{
result = boost::json::value_from( scope.*D.pointer );
found = true;
}
});
if( !found )
{
throw std::invalid_argument(
std::string( "'" ) + std::string( name ) + "': no such variable" );
}
return result;
}
// set variable
template<class T> void set_impl( T & t, boost::string_view /*name*/, boost::json::value const& value )
{
t = boost::json::value_to<T>( value );
}
template<class T> void set_impl( T const & /*t*/, boost::string_view name, boost::json::value const& /*value*/ )
{
throw std::invalid_argument(
std::string( "'" ) + std::string( name ) + "': variable cannot be modified" );
}
template<class Scope> void set( Scope& scope, boost::string_view name, boost::json::value const& value )
{
using Md = boost::describe::describe_members<Scope, boost::describe::mod_public>;
bool found = false;
boost::mp11::mp_for_each<Md>([&](auto D) {
if( !found && name == D.name )
{
set_impl( scope.*D.pointer, name, value );
found = true;
}
});
if( !found )
{
throw std::invalid_argument(
std::string( "'" ) + std::string( name ) + "': no such variable" );
}
}
//
struct globals
{
std::string const help = "Enter a variable name ('x', 'y', 'v', or 'm') to print its value; enter variable=value to assign a new value to a variable. Values are in JSON format.";
int x = 1;
double y = 3.14;
std::vector<int> v{ 1, 2, 3 };
std::map<std::string, double> m{ { "BTC", 44898.68 }, { "ETH", 1386.57 } };
};
BOOST_DESCRIBE_STRUCT( globals, (), (help, x, y, v, m) )
int main()
{
globals g_;
for( ;; )
{
std::cout << "\n> ";
std::string line;
std::getline( std::cin, line );
try
{
std::size_t i = line.find( '=' );
if( i != std::string::npos )
{
set( g_, line.substr( 0, i ), boost::json::parse( line.substr( i + 1 ) ) );
}
else
{
std::cout << get( g_, line ) << std::endl;
}
}
catch( std::exception const& x )
{
std::cout << "Error: " << x.what() << std::endl;
}
}
}