C++ 选择第一个非空元素

Question

[问题根据更新要求更新]
我已经实现了以下函数，它应该首先返回非空元素或抛出异常。
您还能发明更经典、更短的名称，例如“max”、“min”、“pair”吗？

template <typename T>
T select_first_not_empty( const T& a, const T&b )
{
    static T null = T();

    if ( a == null && b == null )
        throw std::runtime_error( "null" );

    return
        a != null ? a : b;
}

int main()
{
    const int a1 = 2;
    const int b1 = 0;

    const int* a2 = 0;
    const int* b2 = new int(5);

    const std::string a3 = "";
    const std::string b3 = "";

    std::cout << select_first_not_empty( a1, b1 ) << std::endl;
    std::cout << select_first_not_empty( a2, b2 ) << std::endl;
    std::cout << select_first_not_empty( a3, b3 ) << std::endl;

    return 0;
}

Answer 1

你可以尝试下一步

template < typename T >
T get_valuable( const T& firstValue, 
                const T& alternateValue, 
                const T& zerroValue = T() )
{
    return firstValue != zerroValue ? firstValue : alternateValue;
}

// usage
char *str = "Something"; // sometimes can be NULL
std::string str2 ( get_valuable( str,  "" ) );

// your function
template <typename T>
T select_first_not_empty( const T& a, 
                          const T& b, 
                          const T& zerroValue = T() )
{
    const T result = get_valuable( a, b, zerroValue );
    if ( result == zerroValue )
    {
        throw std::runtime_error( "null" );
    }
    return result;
}