Discussion: A Constant Struggle
Execute the code to understand the output and gain insights into template argument deduction.
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Run the code
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#include <iostream>#include <type_traits>template <typename T>void byValue(T t){std::cout << std::is_const_v<T>; // true if T is const}template <typename T>void byReference(T &t){std::cout << std::is_const_v<T>; // true if T is const}int main(){int nonConstInt = 0;const int constInt = 0;byValue(nonConstInt);byValue(constInt);byReference(nonConstInt);byReference(constInt);}
Understanding the output
The two function templates byValue and byReference take their parameters by value and by reference, respectively. We then call these two function templates with a non-const and a const int as arguments. In which cases is T deduced as const?
Template parameter
Before we start digging into the deduction rules, let’s clarify two concepts that can be easily mixed up. The T in template <typename T> is called the template parameter. The goal of template argument deduction is to find T. On the other hand, the T and T & in the function signatures byValue(T ...