如何初始化共享复杂初始化代码的多个常量成员变量? [英] How to initialize multiple constant member variables that shares complex initialization code?

问题描述

让我们介绍这个简单的例子:

Let's introduce this simple example:

#include <cmath>

class X
{
public: // Members

    /// A ^ B + A
    int A;

    /// A ^ B + B
    int B;

public: // Specials

    X(
        const int & A,
        const int & B
    )
        : A(A)
        , B(B)
    {
        const auto Pow = static_cast<int>(std::pow(A, B));

        this->A += Pow;
        this->B += Pow;
    }
};

琐事

• 引入的类具有两个成员变量:A和B.
• 它们的值分别为A ^ B + A和A ^ B + B.
• 它们两者共享通用的复杂初始化代码(假设std::pow是复杂的).

Trivia

• Introduced class has two member variables: A and B.
• They take value of A ^ B + A and A ^ B + B, respectively.
• Both of them shares common complex initialization code (let's assume std::pow is complex).

我想同时成为A和B成员const.

如何做到这一点而无需重复复杂的初始化( ie 避免两次调用std::pow)?

How to do that without repeating complex initialization (ie avoid calling std::pow twice)?

#include <cmath>

class X
{
public: // Members

    /// A ^ B + A
    const int A;

    /// A ^ B + B
    const int B;

public: // Helpers

    struct Init
    {
    public: // Members

        int A;
        int B;

    public: // Specials

        Init(
            const int & A,
            const int & B
        )
            : A(A)
            , B(B)
        {
            const auto Pow = static_cast<int>(std::pow(A, B));

            this->A += Pow;
            this->B += Pow;
        }
    };

public: // Specials

    X(
        const Init& Init
    )
        : A(Init.A)
        , B(Init.B)
    {};

    X(
        const int & A,
        const int & B
    )
        : X(Init(
            A,
            B
        ))
    {};
};

1. 创建具有X类的过去版本角色的struct Init.
2. 使X成员const，而使Init成员非const.
3. 使用构造函数委托将构造函数参数重定向到Init.
4. 将非const成员变量从Init移动到X，并将其设置为const.
   • 请注意，由于int是 TriviallyCopyable .
1. Create struct Init that takes role of past version of class X.
2. Make X members const while keep Init members non const.
3. Use constructor delegation to redirect constructor arguments to Init.
4. Move non const member variables from Init to X and make them const.
   • Note there is no std::move as int is TriviallyCopyable.

但是，我的解决方案似乎过于复杂.任何帮助将不胜感激.

However, my solution seems overcomplicated. Any help would be appreciated.

• 制作另一个X成员变量，该成员变量将存储通用代码结果( ie std::pow).
• 在X类之外添加另一级别的间接寻址( eg 为X引入基类).
• Make another X member variable that will store common code result (ie std::pow).
• Add another level of indirection outside X class (eg introduce base class for X).

解决方案可以使用比C ++ 11更新的C ++版本.

Solutions can use newer versions of C++ than C++11.

推荐答案

使用 func1，func2和func3中的逻辑/计算可以根据需要简单或复杂.

The logic/computation in func1, func2, and func3 can be as simple or as complex as you need.

这篇关于如何初始化共享复杂初始化代码的多个常量成员变量?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！