1 //-----------------------------------------------------------------------------
2 // boost-libs variant/test/test3.cpp source file
3 // See http://www.boost.org for updates, documentation, and revision history.
4 //-----------------------------------------------------------------------------
5 //
6 // Copyright (c) 2003
7 // Eric Friedman, Itay Maman
8 //
9 // Distributed under the Boost Software License, Version 1.0. (See
10 // accompanying file LICENSE_1_0.txt or copy at
11 // http://www.boost.org/LICENSE_1_0.txt)
12
13 #include "boost/core/lightweight_test.hpp"
14 #include "boost/variant.hpp"
15
16 #include <iostream>
17 #include <sstream>
18 #include <string>
19
20 /////////////////////////////////////////////////////////////////////
21
22 using boost::variant;
23 using boost::recursive_wrapper;
24 using std::cout;
25 using std::endl;
26
27 /////////////////////////////////////////////////////////////////////
28 /////////////////////////////////////////////////////////////////////
29
30 struct Add;
31 struct Sub;
32
33 typedef variant<int, recursive_wrapper<Add>, recursive_wrapper<Sub> > Expr;
34
35 struct Sub
36 {
37 Sub();
38 Sub(const Expr& l, const Expr& r);
39 Sub(const Sub& other);
40
41 Expr lhs_;
42 Expr rhs_;
43 };
44
45 struct Add
46 {
AddAdd47 Add() { }
AddAdd48 Add(const Expr& l, const Expr& r) : lhs_(l), rhs_(r) { }
AddAdd49 Add(const Add& other) : lhs_(other.lhs_), rhs_(other.rhs_) { }
50
51 Expr lhs_;
52 Expr rhs_;
53 };
54
Sub()55 Sub::Sub() { }
Sub(const Expr & l,const Expr & r)56 Sub::Sub(const Expr& l, const Expr& r) : lhs_(l), rhs_(r) { }
Sub(const Sub & other)57 Sub::Sub(const Sub& other) : lhs_(other.lhs_), rhs_(other.rhs_) { }
58
59
60 //
61 // insert-to operators
62 //
63 std::ostream& operator<<(std::ostream& out, const Sub& a);
64
operator <<(std::ostream & out,const Add & a)65 std::ostream& operator<<(std::ostream& out, const Add& a)
66 {
67 out << '(' << a.lhs_ << '+' << a.rhs_ << ')';
68 return out;
69 }
70
operator <<(std::ostream & out,const Sub & a)71 std::ostream& operator<<(std::ostream& out, const Sub& a)
72 {
73 out << '(' << a.lhs_ << '-' << a.rhs_ << ')';
74 return out;
75 }
76
77 //
78 // Expression evaluation visitor
79 //
80 struct Calculator : boost::static_visitor<int>
81 {
CalculatorCalculator82 Calculator() { }
83
operator ()Calculator84 int operator()(Add& x) const
85 {
86 Calculator calc;
87 int n1 = boost::apply_visitor(calc, x.lhs_);
88 int n2 = boost::apply_visitor(calc, x.rhs_);
89
90 return n1 + n2;
91 }
92
operator ()Calculator93 int operator()(Sub& x) const
94 {
95 return boost::apply_visitor(Calculator(), x.lhs_)
96 - boost::apply_visitor(Calculator(), x.rhs_);
97 }
98
operator ()Calculator99 int operator()(Expr& x) const
100 {
101 Calculator calc;
102 return boost::apply_visitor(calc, x);
103 }
104
operator ()Calculator105 int operator()(int x) const
106 {
107 return x;
108 }
109
110 }; // Calculator
111
112
113 /////////////////////////////////////////////////////////////////////
114
115
main()116 int main()
117 {
118
119 int n = 13;
120 Expr e1( Add(n, Sub(Add(40,2),Add(10,4))) ); //n + (40+2)-(10+14) = n+28
121
122 std::ostringstream e1_str;
123 e1_str << e1;
124
125 BOOST_TEST(e1.type() == boost::typeindex::type_id<Add>());
126 BOOST_TEST(e1_str.str() == "(13+((40+2)-(10+4)))");
127
128 //Evaluate expression
129 int res = boost::apply_visitor(Calculator(), e1);
130 BOOST_TEST(res == n + 28);
131
132 return boost::report_errors();
133 }
134
135