├── .gitignore
├── LICENSE.md
├── README.md
└── polyvar.hpp


/.gitignore:
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 2 | *.slo
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27 | *.exe
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30 | 


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/LICENSE.md:
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 1 | Copyright 2016 Barrett Adair
 2 | 
 3 | Boost Software License - Version 1.0 - August 17th, 2003
 4 | 
 5 | Permission is hereby granted, free of charge, to any person or organization
 6 | obtaining a copy of the software and accompanying documentation covered by
 7 | this license (the "Software") to use, reproduce, display, distribute,
 8 | execute, and transmit the Software, and to prepare derivative works of the
 9 | Software, and to permit third-parties to whom the Software is furnished to
10 | do so, all subject to the following:
11 | 
12 | The copyright notices in the Software and this entire statement, including
13 | the above license grant, this restriction and the following disclaimer,
14 | must be included in all copies of the Software, in whole or in part, and
15 | all derivative works of the Software, unless such copies or derivative
16 | works are solely in the form of machine-executable object code generated by
17 | a source language processor.
18 | 
19 | THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
20 | IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
21 | FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
22 | SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
23 | FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
24 | ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
25 | DEALINGS IN THE SOFTWARE.
26 | 


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/README.md:
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 1 | # polyvar
 2 | polymorphism with value semantics (based on std::variant)
 3 | 
 4 | Example:
 5 | 
 6 | ```cpp
 7 | #include "polyvar.hpp"
 8 | #include <iostream>
 9 | 
10 | struct A {
11 |     char do_something() { return 'A'; }
12 |     int do_something_else(int x) { return x; }
13 | };
14 | 
15 | struct B {
16 |     char do_something() { return 'B'; }
17 |     int do_something_else(int x) { return x + 1; }
18 | };
19 | 
20 | struct C {
21 |     char do_something() { return 'C'; }
22 |     int do_something_else(int x) { return x + 2; }
23 | };
24 | 
25 | // Define a variant template with self-visiting member
26 | // functions to emulate a base class
27 | DEFINE_POLYVAR(my_var,
28 |     (do_something)
29 |     (do_something_else)
30 | );
31 | 
32 | using var = my_var<A, B, C>;
33 | 
34 | int main () {
35 | 
36 |     var v = A{};
37 |     std::cout << v.do_something() << std::endl;
38 |     std::cout << v.do_something_else(0) << std::endl;
39 | 
40 |     v = B{};
41 |     std::cout << v.do_something() << std::endl;
42 |     std::cout << v.do_something_else(1) << std::endl;
43 | 
44 |     v = C{};
45 |     std::cout << v.do_something() << std::endl;
46 |     std::cout << v.do_something_else(2) << std::endl;
47 | }
48 |     
49 | ```
50 | 


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/polyvar.hpp:
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 1 | /*
 2 | Copyright 2016 Barrett Adair
 3 | 
 4 | Distributed under the Boost Software License, Version 1.0.
 5 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
 6 | */
 7 | 
 8 | #ifndef POLYVAR_HPP
 9 | #define POLYVAR_HPP
10 | 
11 | #include <boost/preprocessor/seq/seq.hpp>
12 | #include <boost/preprocessor/seq/elem.hpp>
13 | #include <boost/preprocessor/seq/size.hpp>
14 | #include <boost/preprocessor/repetition/repeat.hpp>
15 | #include <type_traits>
16 | 
17 | #define POLYVAR_USE_BOOST
18 | //#define POLYVAR_USE_MAPBOX
19 | 
20 | #if defined POLYVAR_USE_BOOST
21 | #  include <boost/variant.hpp>
22 | #  define POLYVAR_VARIANT_IMPL boost::variant
23 | #  define POLYVAR_USING \
24 |         using POLYVAR_VARIANT_IMPL<Ts...>::variant; \
25 |         using POLYVAR_VARIANT_IMPL<Ts...>::operator=; \
26 |         using POLYVAR_VARIANT_IMPL<Ts...>::which; \
27 |         using POLYVAR_VARIANT_IMPL<Ts...>::empty; \
28 |         using POLYVAR_VARIANT_IMPL<Ts...>::type; \
29 | /**/
30 | #  define POLYVAR_VISIT_IMPL boost::apply_visitor
31 | #elif defined POLYVAR_USE_MAPBOX
32 | // include it your damn self
33 | #  define POLYVAR_VARIANT_IMPL mapbox::util::variant
34 | #  define POLYVAR_VISIT_IMPL mapbox::util::apply_visitor
35 | #  define POLYVAR_USING \
36 |         using POLYVAR_VARIANT_IMPL<Ts...>::variant; \
37 |         using POLYVAR_VARIANT_IMPL<Ts...>::operator=; \
38 |         using POLYVAR_VARIANT_IMPL<Ts...>::which; \
39 |         using POLYVAR_VARIANT_IMPL<Ts...>::empty; \
40 |         using POLYVAR_VARIANT_IMPL<Ts...>::type; \
41 | #else
42 | #  include <variant>
43 | #  define POLYVAR_VARIANT_IMPL std::variant
44 | #  define POLYVAR_VISIT_IMPL std::visit
45 | // TODO - check these
46 | #  define POLYVAR_USING \
47 |         using POLYVAR_VARIANT_IMPL<Ts...>::variant; \
48 |         using POLYVAR_VARIANT_IMPL<Ts...>::operator=; \
49 |         using POLYVAR_VARIANT_IMPL<Ts...>::which; \
50 |         using POLYVAR_VARIANT_IMPL<Ts...>::empty; \
51 |         using POLYVAR_VARIANT_IMPL<Ts...>::type; \
52 | /**/
53 | #endif
54 | 
55 | #define DEFINE_POLYVAR(name, ...) \
56 | template<typename... Ts> \
57 | struct name : public POLYVAR_VARIANT_IMPL<Ts...> { \
58 | \
59 |     using base = POLYVAR_VARIANT_IMPL<Ts...>; \
60 |     POLYVAR_USING \
61 | \
62 |     BOOST_PP_REPEAT(BOOST_PP_SEQ_SIZE(__VA_ARGS__), POLYVAR_MEMFNS, __VA_ARGS__) \
63 | } \
64 | /**/
65 | 
66 | #define POLYVAR_MEMFNS(z, i, seq) POLYVAR_MEMFNS_I(BOOST_PP_SEQ_ELEM(i,seq))
67 | 
68 | #define POLYVAR_MEMFNS_I(name)                                 \
69 |     template<typename... Args>                                 \
70 |     constexpr decltype(auto) name(Args&&... args) {            \
71 |         return POLYVAR_VISIT_IMPL([&](auto& v){                \
72 |             return v.name(                                     \
73 |                 static_cast<Args&&>(args)...);}, *this);       \
74 |     }                                                          \
75 | /**/
76 | 
77 | #endif // #ifndef POLYVAR_HPP
78 | 


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