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//-----------------------------------------------------------------------------
// boost-libs variant/test/test3.cpp source file
// See http://www.boost.org for updates, documentation, and revision history.
//-----------------------------------------------------------------------------
//
// Copyright (c) 2003
// Eric Friedman, Itay Maman
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
#include "boost/test/minimal.hpp"
#include "boost/variant.hpp"
#include <iostream>
#include <sstream>
#include <string>
/////////////////////////////////////////////////////////////////////
using boost::variant;
using boost::recursive_wrapper;
using std::cout;
using std::endl;
/////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////
struct Add;
struct Sub;
typedef variant<int, recursive_wrapper<Add>, recursive_wrapper<Sub> > Expr;
struct Sub
{
Sub();
Sub(const Expr& l, const Expr& r);
Sub(const Sub& other);
Expr lhs_;
Expr rhs_;
};
struct Add
{
Add() { }
Add(const Expr& l, const Expr& r) : lhs_(l), rhs_(r) { }
Add(const Add& other) : lhs_(other.lhs_), rhs_(other.rhs_) { }
Expr lhs_;
Expr rhs_;
};
Sub::Sub() { }
Sub::Sub(const Expr& l, const Expr& r) : lhs_(l), rhs_(r) { }
Sub::Sub(const Sub& other) : lhs_(other.lhs_), rhs_(other.rhs_) { }
//
// insert-to operators
//
std::ostream& operator<<(std::ostream& out, const Sub& a);
std::ostream& operator<<(std::ostream& out, const Add& a)
{
out << '(' << a.lhs_ << '+' << a.rhs_ << ')';
return out;
}
std::ostream& operator<<(std::ostream& out, const Sub& a)
{
out << '(' << a.lhs_ << '-' << a.rhs_ << ')';
return out;
}
//
// Expression evaluation visitor
//
struct Calculator : boost::static_visitor<int>
{
Calculator() { }
int operator()(Add& x) const
{
Calculator calc;
int n1 = boost::apply_visitor(calc, x.lhs_);
int n2 = boost::apply_visitor(calc, x.rhs_);
return n1 + n2;
}
int operator()(Sub& x) const
{
return boost::apply_visitor(Calculator(), x.lhs_)
- boost::apply_visitor(Calculator(), x.rhs_);
}
int operator()(Expr& x) const
{
Calculator calc;
return boost::apply_visitor(calc, x);
}
int operator()(int x) const
{
return x;
}
}; // Calculator
/////////////////////////////////////////////////////////////////////
int test_main(int, char* [])
{
int n = 13;
Expr e1( Add(n, Sub(Add(40,2),Add(10,4))) ); //n + (40+2)-(10+14) = n+28
std::ostringstream e1_str;
e1_str << e1;
BOOST_CHECK(e1.type() == typeid(Add));
BOOST_CHECK(e1_str.str() == "(13+((40+2)-(10+4)))");
//Evaluate expression
int res = boost::apply_visitor(Calculator(), e1);
BOOST_CHECK(res == n + 28);
return 0;
}
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