40 lines
1.8 KiB
C++
40 lines
1.8 KiB
C++
// fig15_18.cpp
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// Constraining a variadic-function-template parameter pack to
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// elements of the same type.
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#include <concepts>
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#include <iostream>
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#include <string>
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template <typename T, typename... Us>
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concept SameTypeElements = (std::same_as<T, Us> && ...);
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// add one or more arguments with a fold expression
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template <typename FirstItem, typename... RemainingItems>
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requires SameTypeElements<FirstItem, RemainingItems...>
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auto foldingSum(FirstItem first, RemainingItems... theRest) {
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return (first + ... + theRest); // expand the parameter
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}
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int main() {
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using namespace std::literals;
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foldingSum(1, 2, 3); // valid: all are int values
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foldingSum("s"s, "u"s, "m"s); // valid: all are std::string objects
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foldingSum(1, 2.2, "hello"s); // error: three different types
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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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**************************************************************************/ |