72 lines
3.1 KiB
C++
72 lines
3.1 KiB
C++
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// fig15_21.cpp
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// Adding and removing type attributes with type metafunctions.
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#include <fmt/format.h>
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#include <iostream>
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#include <type_traits>
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// add const to a type T
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template <typename T>
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struct my_add_const {
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using type = const T;
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};
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// general case: no pointer in type, so set nested type variable to T
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template <typename T>
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struct my_remove_ptr {
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using type = T;
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};
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// partial template specialization: T is a pointer type, so remove *
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template <typename T>
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struct my_remove_ptr<T*> {
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using type = T;
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};
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int main() {
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std::cout << fmt::format("{}\n{}{}\n{}{}\n\n",
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"ADD CONST TO A TYPE VIA A CUSTOM TYPE METAFUNCTION",
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"std::is_same_v<const int, my_add_const<int>::type>: ",
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std::is_same_v<const int, my_add_const<int>::type>,
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"std::is_same_v<int* const, my_add_const<int*>::type>: ",
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std::is_same_v<int* const, my_add_const<int*>::type>);
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std::cout << fmt::format("{}\n{}{}\n{}{}\n\n",
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"REMOVE POINTER FROM TYPES VIA A CUSTOM TYPE METAFUNCTION",
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"std::is_same_v<int, my_remove_ptr<int>::type>: ",
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std::is_same_v<int, my_remove_ptr<int>::type>,
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"std::is_same_v<int, my_remove_ptr<int*>::type>: ",
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std::is_same_v<int, my_remove_ptr<int*>::type>);
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std::cout << fmt::format("{}\n{}{}\n{}{}\n\n",
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"ADD REFERENCES TO TYPES USING STANDARD TYPE TRAITS",
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"std::is_same_v<int&, std::add_lvalue_reference<int>::type>: ",
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std::is_same_v<int&, std::add_lvalue_reference<int>::type>,
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"std::is_same_v<int&&, std::add_rvalue_reference<int>::type>: ",
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std::is_same_v<int&&, std::add_rvalue_reference<int>::type>);
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std::cout << fmt::format("{}\n{}{}\n{}{}\n{}{}\n",
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"REMOVE REFERENCES FROM TYPES USING STANDARD TYPE TRAITS",
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"std::is_same_v<int, std::remove_reference<int>::type>: ",
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std::is_same_v<int, std::remove_reference<int>::type>,
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"std::is_same_v<int, std::remove_reference<int&>::type>: ",
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std::is_same_v<int, std::remove_reference<int&>::type>,
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"std::is_same_v<int, std::remove_reference<int&&>::type>: ",
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std::is_same_v<int, std::remove_reference<int&&>::type>);
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}
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/**************************************************************************
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* (C) Copyright 1992-2022 by Deitel & Associates, Inc. and *
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* Pearson Education, Inc. All Rights Reserved. *
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* *
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* DISCLAIMER: The authors and publisher of this book have used their *
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* best efforts in preparing the book. These efforts include the *
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* development, research, and testing of the theories and programs *
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* to determine their effectiveness. The authors and publisher make *
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* no warranty of any kind, expressed or implied, with regard to these *
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* programs or to the documentation contained in these books. The authors *
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* and publisher shall not be liable in any event for incidental or *
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* consequential damages in connection with, or arising out of, the *
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* furnishing, performance, or use of these programs. *
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**************************************************************************/
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