CPlusPlus – Constexpr, Delete, Right Value Reference

Constexpr : Know Value At Compile Time

int main(int argc, char** argv )
{
    int size0;
    constexpr auto size1 = 10;
    //constexpr auto size2 = size0; //error: constexpr variable 'size2' must be initialized by a constant expression
    return 0;
}

Mark Function Delete To Avoid Data Type Conversion

void ShowValue(double value)
{
    std::cout << "value: " << value << std::endl;
}
void ShowValue(int value) = delete;
void ShowValue(char value) = delete;

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

//    ShowValue( 1 ); // compile error
//    ShowValue( 'a' );  // compile error
    ShowValue( 1.2 );


    return a.exec();
}

Left Value Reference And Right Value Reference For Function Parameter

void ShowValue(double &&value)
{
    std::cout << "right value reference: " << value << std::endl;
}

void ShowValue(double &value)
{
    std::cout << "left value reference: " << value << std::endl;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    auto value = 1.2;
    ShowValue( value );
    ShowValue( 1.4 );

    return a.exec();
}
/*
left value reference: 1.2
right value reference: 1.4
*/