auto, decltype(auto), auto& and auto&&, C++ (vc++)

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//Microsoft (R) C/C++ Optimizing Compiler Version 19.00.23506 for x64

#include <iostream>
#include <type_traits>
#include <cstring>

int main() {

// alias for 'lvalue reference to array of 15 const char'
    using lvalue_ref_to_array = std::add_lvalue_reference< const char[15] >::type ;

// type of name is deduced using the rules for template argument deduction for a function call
    // where the parameter is passed by value.
    // the type of the expression "The value is: " is 'array of 15 const char'
    // ergo deduced type is 'pointer to const char'
    auto name = "The value is: ";
    static_assert( std::is_same< decltype(name), const char* >::value,
                   "type of name should be 'pointer to const char'" ) ;
    std::cout << sizeof(name) << '\n' ; // sizeof( const char*)

// type of name2 is deduced using the deduction rules for decltype
    // the type of the expression "The value is: " is 'array of 15 const char'
    // and its value category is lvalue.
    // ergo, deduced type is 'lvalue reference to array of 15 const char'
    decltype(auto) name2 = "The value is: ";
    static_assert( std::is_same< decltype(name2), lvalue_ref_to_array >::value,
                   "type of name2 should be 'reference to array of 15 const char'" ) ;
    std::cout << sizeof(name2) << '\n' ; // sizeof( const char[15] ) ie. 15

// type of name is deduced using the rules for template argument deduction for a function call
    // where the parameter is passed by lvalue reference.
    // the type of the expression "The value is: " is 'array of 15 const char'
    // ergo, deduced type is 'lvalue reference to array of 15 const char'
    auto& name3 = "The value is: ";
    static_assert( std::is_same< decltype(name3), lvalue_ref_to_array >::value,
                   "type of name3 should be 'reference to array of 15 const char'" ) ;
    std::cout << sizeof(name3) << '\n' ; // sizeof( const char[15] ) ie. 15

// type of name is deduced using the rules for template argument deduction for a function call
    // where the parameter is passed by forwarding reference.
    // the type of the expression "The value is: " is 'array of 15 const char'
    // and its value category is lvalue.
    // ergo, deduced type is 'lvalue reference to array of 15 const char'
    auto&& name4 = "The value is: ";
    static_assert( std::is_same< decltype(name4), lvalue_ref_to_array >::value,
                   "type of name4 should be 'reference to array of 15 const char'" ) ;
    std::cout << sizeof(name4) << '\n' ; // sizeof( const char[15] ) ie. 15
}

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Compilation time: 6,32 sec, absolute running time: 0,33 sec, absolute service time: 6,67 sec