[英]How to initialize const member , that are not static
I know how to initialize const member in the initializer list, but that requires to know the value to be assigned already when calling the constructor. 我知道如何在初始化列表中初始化const成员,但这需要知道在调用构造函数时已分配的值。 From what I understand, in java it's possible to initialize a final member in the constructor body, but I haven't seen an equivalent in c++ ( Java's final vs. C++'s const )
据我了解,在Java中可以在构造函数主体中初始化最终成员,但我还没有看到C ++中的等效成员( Java的最终版本与C ++的const )
But what to do when the initialization is relatively complex? 但是,当初始化相对复杂时该怎么办? The best I could come up, is to have an initialization function that returns directly an instance.
我能想到的最好的办法是拥有一个直接返回实例的初始化函数。 Is there something more concise?
还有更简洁的东西吗?
Here is an example ( https://ideone.com/TXxIHo ) 这是一个示例( https://ideone.com/TXxIHo )
class Multiplier
{
const int mFactor1;
const int mFactor2;
static void initializationLogic (int & a, int & b, const int c )
{
a = c * 5;
b = a * 2;
}
public:
Multiplier (const int & value1, const int & value2)
: mFactor1(value1), mFactor2(value2)
{};
/*
//this constructor doesn't initialize the const members
Multiplier (const int & value)
{
initializationLogic(mFactor1,mFactor2, value);
};
*/
//this initializes the const members, but it's not a constructor
static Multiplier getMultiplierInstance (const int & value)
{
int f1, f2;
initializationLogic(f1,f2, value);
Multiplier obj(f1,f2);
return obj;
}
You can delegate object construction to a dedicated constructor accepting an instance of helper class preparing all the necessary parameters: 您可以将对象构造委托给专用的构造函数,该构造函数接受准备所有必要参数的helper类的实例:
private: class
Init_Helper final
{
private: int m_value1;
private: int m_value2;
public: explicit Init_Helper(const int c)
{
m_value1 = c * 5;
m_value2 = m_value1 * 2;
// more init logic goes here...
}
public: int const & Get_Value1(void) const
{
return m_value1;
}
public: int const & Get_Value2(void) const
{
return m_value2;
}
};
public: explicit Multiplier(const int c)
: Multiplier{Init_Helper{c}}
{}
private: explicit Multiplier(Init_Helper && helper)
: mFactor1{helper.Get_Value1()}, mFactor2{helper.Get_Value2()}
{}
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