├── README.md ├── demo.cpp ├── LICENSE └── is_call_possible.hpp /README.md: -------------------------------------------------------------------------------- 1 | is_call_possible 2 | ================ 3 | 4 | C++03 functionality for checking for the existence of a member function with a given name and signature. 5 | 6 | Inspired by Roman Perepelitsa's presentation from [`comp.lang.c++.moderated`](https://groups.google.com/d/msg/comp.lang.c++.moderated/T3x6lvmvvkQ/mfY5VTDJ--UJ) which was based on the [original implementation here](http://www.rsdn.ru/forum/cpp/2759773.1.aspx). 7 | 8 | Demo 9 | ---- 10 | 11 | ```c++ 12 | #include "is_call_possible.hpp" 13 | #include 14 | #include 15 | #include 16 | 17 | // define a trait to check for the possibility of calling operator() on a given type 18 | DEFINE_IS_CALL_POSSIBLE(is_call_possible, operator()) 19 | 20 | // test cases 21 | struct Foo 22 | { 23 | void operator()(double) const {} 24 | void operator()(std::string) const {} 25 | }; 26 | 27 | struct Bar : Foo 28 | { 29 | int operator()(int) 30 | { 31 | return 0; 32 | } 33 | }; 34 | 35 | int main() 36 | { 37 | // Foo has operator() which takes a double and returns void 38 | assert((is_call_possible::value)); 39 | 40 | // Foo has operator() which takes int and returns void 41 | assert((is_call_possible::value)); 42 | 43 | // Foo has operator() which can convert const char * to string and return void 44 | assert((is_call_possible::value)); 45 | 46 | // Foo has no operator() which can take a void * 47 | assert((!is_call_possible::value)); 48 | 49 | // Bar inherits Foo's operator() which takes a double and returns void 50 | assert((is_call_possible::value)); 51 | 52 | // Bar has operator() which takes int and converts its int result to void 53 | assert((is_call_possible::value)); 54 | 55 | // Bar has operator() which takes int but cannot convert const char * to int 56 | assert((!is_call_possible::value)); 57 | 58 | // Neither Bar nor Foo has an operator() which can take void * 59 | assert((!is_call_possible::value)); 60 | 61 | // Bar has operator() which takes int and returns int 62 | assert((is_call_possible::value)); 63 | 64 | return 0; 65 | } 66 | ``` 67 | -------------------------------------------------------------------------------- /demo.cpp: -------------------------------------------------------------------------------- 1 | #include "is_call_possible.hpp" 2 | #include 3 | #include 4 | #include 5 | #include 6 | #include 7 | 8 | // define a trait to check for the possibility of calling operator() on a given type 9 | DEFINE_IS_CALL_POSSIBLE(is_call_possible, operator()) 10 | 11 | // define a trait to check for the possibility of calling baz on a given type 12 | DEFINE_IS_CALL_POSSIBLE(is_baz_possible, baz); 13 | 14 | // test cases 15 | struct foo 16 | { 17 | void operator()(double) const {} 18 | void operator()(std::string) const {} 19 | }; 20 | 21 | struct bar : foo 22 | { 23 | int operator()(int) 24 | { 25 | return 0; 26 | } 27 | 28 | float baz(std::vector) 29 | { 30 | return 13; 31 | } 32 | }; 33 | 34 | int main() 35 | { 36 | // foo has operator() which takes a double and returns void 37 | assert((is_call_possible::value)); 38 | 39 | // foo has operator() which takes int and returns void 40 | assert((is_call_possible::value)); 41 | 42 | // foo has operator() which can convert const char * to string and return void 43 | assert((is_call_possible::value)); 44 | 45 | // foo has no operator() which can take a void * 46 | assert((!is_call_possible::value)); 47 | 48 | // bar inherits foo's operator() which takes a double and returns void 49 | assert((is_call_possible::value)); 50 | 51 | // bar has operator() which takes int and converts its int result to void 52 | assert((is_call_possible::value)); 53 | 54 | // bar has operator() which takes int but cannot convert const char * to int 55 | assert((!is_call_possible::value)); 56 | 57 | // neither bar nor foo has an operator() which can take void * 58 | assert((!is_call_possible::value)); 59 | 60 | // bar has operator() which takes int and returns int 61 | assert((is_call_possible::value)); 62 | 63 | // foo has no baz member function 64 | assert((!is_baz_possible)>::value)); 65 | 66 | // bar has member function baz which takes std::vector and returns float 67 | assert((is_baz_possible)>::value)); 68 | 69 | // bar::baz can't be called with std::list 70 | assert((!is_baz_possible)>::value)); 71 | 72 | return 0; 73 | } 74 | 75 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | 2 | Apache License 3 | Version 2.0, January 2004 4 | http://www.apache.org/licenses/ 5 | 6 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 7 | 8 | 1. Definitions. 9 | 10 | "License" shall mean the terms and conditions for use, reproduction, 11 | and distribution as defined by Sections 1 through 9 of this document. 12 | 13 | "Licensor" shall mean the copyright owner or entity authorized by 14 | the copyright owner that is granting the License. 15 | 16 | "Legal Entity" shall mean the union of the acting entity and all 17 | other entities that control, are controlled by, or are under common 18 | control with that entity. For the purposes of this definition, 19 | "control" means (i) the power, direct or indirect, to cause the 20 | direction or management of such entity, whether by contract or 21 | otherwise, or (ii) ownership of fifty percent (50%) or more of the 22 | outstanding shares, or (iii) beneficial ownership of such entity. 23 | 24 | "You" (or "Your") shall mean an individual or Legal Entity 25 | exercising permissions granted by this License. 26 | 27 | "Source" form shall mean the preferred form for making modifications, 28 | including but not limited to software source code, documentation 29 | source, and configuration files. 30 | 31 | "Object" form shall mean any form resulting from mechanical 32 | transformation or translation of a Source form, including but 33 | not limited to compiled object code, generated documentation, 34 | and conversions to other media types. 35 | 36 | "Work" shall mean the work of authorship, whether in Source or 37 | Object form, made available under the License, as indicated by a 38 | copyright notice that is included in or attached to the work 39 | (an example is provided in the Appendix below). 40 | 41 | "Derivative Works" shall mean any work, whether in Source or Object 42 | form, that is based on (or derived from) the Work and for which the 43 | editorial revisions, annotations, elaborations, or other modifications 44 | represent, as a whole, an original work of authorship. For the purposes 45 | of this License, Derivative Works shall not include works that remain 46 | separable from, or merely link (or bind by name) to the interfaces of, 47 | the Work and Derivative Works thereof. 48 | 49 | "Contribution" shall mean any work of authorship, including 50 | the original version of the Work and any modifications or additions 51 | to that Work or Derivative Works thereof, that is intentionally 52 | submitted to Licensor for inclusion in the Work by the copyright owner 53 | or by an individual or Legal Entity authorized to submit on behalf of 54 | the copyright owner. For the purposes of this definition, "submitted" 55 | means any form of electronic, verbal, or written communication sent 56 | to the Licensor or its representatives, including but not limited to 57 | communication on electronic mailing lists, source code control systems, 58 | and issue tracking systems that are managed by, or on behalf of, the 59 | Licensor for the purpose of discussing and improving the Work, but 60 | excluding communication that is conspicuously marked or otherwise 61 | designated in writing by the copyright owner as "Not a Contribution." 62 | 63 | "Contributor" shall mean Licensor and any individual or Legal Entity 64 | on behalf of whom a Contribution has been received by Licensor and 65 | subsequently incorporated within the Work. 66 | 67 | 2. Grant of Copyright License. Subject to the terms and conditions of 68 | this License, each Contributor hereby grants to You a perpetual, 69 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 70 | copyright license to reproduce, prepare Derivative Works of, 71 | publicly display, publicly perform, sublicense, and distribute the 72 | Work and such Derivative Works in Source or Object form. 73 | 74 | 3. Grant of Patent License. Subject to the terms and conditions of 75 | this License, each Contributor hereby grants to You a perpetual, 76 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 77 | (except as stated in this section) patent license to make, have made, 78 | use, offer to sell, sell, import, and otherwise transfer the Work, 79 | where such license applies only to those patent claims licensable 80 | by such Contributor that are necessarily infringed by their 81 | Contribution(s) alone or by combination of their Contribution(s) 82 | with the Work to which such Contribution(s) was submitted. If You 83 | institute patent litigation against any entity (including a 84 | cross-claim or counterclaim in a lawsuit) alleging that the Work 85 | or a Contribution incorporated within the Work constitutes direct 86 | or contributory patent infringement, then any patent licenses 87 | granted to You under this License for that Work shall terminate 88 | as of the date such litigation is filed. 89 | 90 | 4. Redistribution. You may reproduce and distribute copies of the 91 | Work or Derivative Works thereof in any medium, with or without 92 | modifications, and in Source or Object form, provided that You 93 | meet the following conditions: 94 | 95 | (a) You must give any other recipients of the Work or 96 | Derivative Works a copy of this License; and 97 | 98 | (b) You must cause any modified files to carry prominent notices 99 | stating that You changed the files; and 100 | 101 | (c) You must retain, in the Source form of any Derivative Works 102 | that You distribute, all copyright, patent, trademark, and 103 | attribution notices from the Source form of the Work, 104 | excluding those notices that do not pertain to any part of 105 | the Derivative Works; and 106 | 107 | (d) If the Work includes a "NOTICE" text file as part of its 108 | distribution, then any Derivative Works that You distribute must 109 | include a readable copy of the attribution notices contained 110 | within such NOTICE file, excluding those notices that do not 111 | pertain to any part of the Derivative Works, in at least one 112 | of the following places: within a NOTICE text file distributed 113 | as part of the Derivative Works; within the Source form or 114 | documentation, if provided along with the Derivative Works; or, 115 | within a display generated by the Derivative Works, if and 116 | wherever such third-party notices normally appear. The contents 117 | of the NOTICE file are for informational purposes only and 118 | do not modify the License. You may add Your own attribution 119 | notices within Derivative Works that You distribute, alongside 120 | or as an addendum to the NOTICE text from the Work, provided 121 | that such additional attribution notices cannot be construed 122 | as modifying the License. 123 | 124 | You may add Your own copyright statement to Your modifications and 125 | may provide additional or different license terms and conditions 126 | for use, reproduction, or distribution of Your modifications, or 127 | for any such Derivative Works as a whole, provided Your use, 128 | reproduction, and distribution of the Work otherwise complies with 129 | the conditions stated in this License. 130 | 131 | 5. Submission of Contributions. Unless You explicitly state otherwise, 132 | any Contribution intentionally submitted for inclusion in the Work 133 | by You to the Licensor shall be under the terms and conditions of 134 | this License, without any additional terms or conditions. 135 | Notwithstanding the above, nothing herein shall supersede or modify 136 | the terms of any separate license agreement you may have executed 137 | with Licensor regarding such Contributions. 138 | 139 | 6. Trademarks. This License does not grant permission to use the trade 140 | names, trademarks, service marks, or product names of the Licensor, 141 | except as required for reasonable and customary use in describing the 142 | origin of the Work and reproducing the content of the NOTICE file. 143 | 144 | 7. Disclaimer of Warranty. Unless required by applicable law or 145 | agreed to in writing, Licensor provides the Work (and each 146 | Contributor provides its Contributions) on an "AS IS" BASIS, 147 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 148 | implied, including, without limitation, any warranties or conditions 149 | of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A 150 | PARTICULAR PURPOSE. You are solely responsible for determining the 151 | appropriateness of using or redistributing the Work and assume any 152 | risks associated with Your exercise of permissions under this License. 153 | 154 | 8. Limitation of Liability. In no event and under no legal theory, 155 | whether in tort (including negligence), contract, or otherwise, 156 | unless required by applicable law (such as deliberate and grossly 157 | negligent acts) or agreed to in writing, shall any Contributor be 158 | liable to You for damages, including any direct, indirect, special, 159 | incidental, or consequential damages of any character arising as a 160 | result of this License or out of the use or inability to use the 161 | Work (including but not limited to damages for loss of goodwill, 162 | work stoppage, computer failure or malfunction, or any and all 163 | other commercial damages or losses), even if such Contributor 164 | has been advised of the possibility of such damages. 165 | 166 | 9. Accepting Warranty or Additional Liability. While redistributing 167 | the Work or Derivative Works thereof, You may choose to offer, 168 | and charge a fee for, acceptance of support, warranty, indemnity, 169 | or other liability obligations and/or rights consistent with this 170 | License. However, in accepting such obligations, You may act only 171 | on Your own behalf and on Your sole responsibility, not on behalf 172 | of any other Contributor, and only if You agree to indemnify, 173 | defend, and hold each Contributor harmless for any liability 174 | incurred by, or claims asserted against, such Contributor by reason 175 | of your accepting any such warranty or additional liability. 176 | 177 | END OF TERMS AND CONDITIONS 178 | 179 | -------------------------------------------------------------------------------- /is_call_possible.hpp: -------------------------------------------------------------------------------- 1 | #pragma once 2 | 3 | // inspired by Roman Perepelitsa's presentation from comp.lang.c++.moderated 4 | // based on the implementation here: http://www.rsdn.ru/forum/cpp/2759773.1.aspx 5 | namespace is_call_possible_detail 6 | { 7 | 8 | template 9 | struct add_reference 10 | { 11 | typedef T& type; 12 | }; 13 | 14 | template 15 | struct add_reference 16 | { 17 | typedef T& type; 18 | }; 19 | 20 | } // end is_call_possible_detail 21 | 22 | #define DEFINE_HAS_MEMBER_FUNCTION(trait_name, member_function_name) \ 23 | template class trait_name; \ 24 | \ 25 | template \ 26 | class trait_name \ 27 | { \ 28 | class yes { char m; }; \ 29 | class no { yes m[2]; }; \ 30 | struct base_mixin \ 31 | { \ 32 | Result member_function_name(); \ 33 | }; \ 34 | struct base : public T, public base_mixin {}; \ 35 | template class helper{}; \ 36 | template \ 37 | static no deduce(U*, helper* = 0); \ 38 | static yes deduce(...); \ 39 | public: \ 40 | static const bool value = sizeof(yes) == sizeof(deduce(static_cast(0))); \ 41 | }; \ 42 | \ 43 | template \ 44 | class trait_name \ 45 | { \ 46 | class yes { char m; }; \ 47 | class no { yes m[2]; }; \ 48 | struct base_mixin \ 49 | { \ 50 | Result member_function_name(Arg); \ 51 | }; \ 52 | struct base : public T, public base_mixin {}; \ 53 | template class helper{}; \ 54 | template \ 55 | static no deduce(U*, helper* = 0); \ 56 | static yes deduce(...); \ 57 | public: \ 58 | static const bool value = sizeof(yes) == sizeof(deduce(static_cast(0))); \ 59 | }; \ 60 | \ 61 | template \ 62 | class trait_name \ 63 | { \ 64 | class yes { char m; }; \ 65 | class no { yes m[2]; }; \ 66 | struct base_mixin \ 67 | { \ 68 | Result member_function_name(Arg1,Arg2); \ 69 | }; \ 70 | struct base : public T, public base_mixin {}; \ 71 | template class helper{}; \ 72 | template \ 73 | static no deduce(U*, helper* = 0); \ 74 | static yes deduce(...); \ 75 | public: \ 76 | static const bool value = sizeof(yes) == sizeof(deduce(static_cast(0))); \ 77 | }; \ 78 | \ 79 | template \ 80 | class trait_name \ 81 | { \ 82 | class yes { char m; }; \ 83 | class no { yes m[2]; }; \ 84 | struct base_mixin \ 85 | { \ 86 | Result member_function_name(Arg1,Arg2,Arg3); \ 87 | }; \ 88 | struct base : public T, public base_mixin {}; \ 89 | template class helper{}; \ 90 | template \ 91 | static no deduce(U*, helper* = 0); \ 92 | static yes deduce(...); \ 93 | public: \ 94 | static const bool value = sizeof(yes) == sizeof(deduce(static_cast(0))); \ 95 | }; \ 96 | \ 97 | template \ 98 | class trait_name \ 99 | { \ 100 | class yes { char m; }; \ 101 | class no { yes m[2]; }; \ 102 | struct base_mixin \ 103 | { \ 104 | Result member_function_name(Arg1,Arg2,Arg3,Arg4); \ 105 | }; \ 106 | struct base : public T, public base_mixin {}; \ 107 | template class helper{}; \ 108 | template \ 109 | static no deduce(U*, helper* = 0); \ 110 | static yes deduce(...); \ 111 | public: \ 112 | static const bool value = sizeof(yes) == sizeof(deduce(static_cast(0))); \ 113 | }; 114 | 115 | namespace is_call_possible_detail 116 | { 117 | template class void_exp_result {}; 118 | 119 | template 120 | U const& operator,(U const&, void_exp_result); 121 | 122 | template 123 | U& operator,(U&, void_exp_result); 124 | 125 | template 126 | struct clone_constness 127 | { 128 | typedef dest_type type; 129 | }; 130 | 131 | template 132 | struct clone_constness 133 | { 134 | typedef const dest_type type; 135 | }; 136 | } 137 | 138 | #define DEFINE_IS_CALL_POSSIBLE(trait_name, member_function_name) \ 139 | namespace trait_name##_detail \ 140 | { \ 141 | DEFINE_HAS_MEMBER_FUNCTION(has_member, member_function_name) \ 142 | } \ 143 | \ 144 | template \ 145 | struct trait_name \ 146 | { \ 147 | private: \ 148 | class yes {}; \ 149 | class no { yes m[2]; }; \ 150 | struct derived : public T \ 151 | { \ 152 | using T::member_function_name; \ 153 | no member_function_name(...) const; \ 154 | }; \ 155 | \ 156 | typedef typename is_call_possible_detail::clone_constness::type derived_type; \ 157 | \ 158 | template \ 159 | struct return_value_check \ 160 | { \ 161 | static yes deduce(Result); \ 162 | static no deduce(...); \ 163 | static no deduce(no); \ 164 | static no deduce(is_call_possible_detail::void_exp_result); \ 165 | }; \ 166 | \ 167 | template \ 168 | struct return_value_check \ 169 | { \ 170 | static yes deduce(...); \ 171 | static no deduce(no); \ 172 | }; \ 173 | \ 174 | template \ 175 | struct impl \ 176 | { \ 177 | static const bool value = false; \ 178 | }; \ 179 | \ 180 | template \ 181 | struct impl \ 182 | { \ 183 | static typename is_call_possible_detail::add_reference::type test_me; \ 184 | static typename is_call_possible_detail::add_reference::type arg; \ 185 | \ 186 | static const bool value = \ 187 | sizeof( \ 188 | return_value_check::deduce( \ 189 | (test_me.member_function_name(arg), is_call_possible_detail::void_exp_result()) \ 190 | ) \ 191 | ) == sizeof(yes); \ 192 | }; \ 193 | \ 194 | template \ 195 | struct impl \ 196 | { \ 197 | static typename is_call_possible_detail::add_reference::type test_me; \ 198 | static typename is_call_possible_detail::add_reference::type arg1; \ 199 | static typename is_call_possible_detail::add_reference::type arg2; \ 200 | \ 201 | static const bool value = \ 202 | sizeof( \ 203 | return_value_check::deduce( \ 204 | (test_me.member_function_name(arg1,arg2), is_call_possible_detail::void_exp_result()) \ 205 | ) \ 206 | ) == sizeof(yes); \ 207 | }; \ 208 | \ 209 | template \ 210 | struct impl \ 211 | { \ 212 | static typename is_call_possible_detail::add_reference::type test_me; \ 213 | static typename is_call_possible_detail::add_reference::type arg1; \ 214 | static typename is_call_possible_detail::add_reference::type arg2; \ 215 | static typename is_call_possible_detail::add_reference::type arg3; \ 216 | \ 217 | static const bool value = \ 218 | sizeof( \ 219 | return_value_check::deduce( \ 220 | (test_me.member_function_name(arg1,arg2,arg3), is_call_possible_detail::void_exp_result()) \ 221 | ) \ 222 | ) == sizeof(yes); \ 223 | }; \ 224 | \ 225 | template \ 226 | struct impl \ 227 | { \ 228 | static typename is_call_possible_detail::add_reference::type test_me; \ 229 | static typename is_call_possible_detail::add_reference::type arg1; \ 230 | static typename is_call_possible_detail::add_reference::type arg2; \ 231 | static typename is_call_possible_detail::add_reference::type arg3; \ 232 | static typename is_call_possible_detail::add_reference::type arg4; \ 233 | \ 234 | static const bool value = \ 235 | sizeof( \ 236 | return_value_check::deduce( \ 237 | (test_me.member_function_name(arg1,arg2,arg3,arg4), is_call_possible_detail::void_exp_result()) \ 238 | ) \ 239 | ) == sizeof(yes); \ 240 | }; \ 241 | \ 242 | public: \ 243 | static const bool value = impl::value, Signature>::value; \ 244 | }; 245 | 246 | --------------------------------------------------------------------------------