相当于代数数据类型的C ++? [英] C++ equivalent of algebraic datatype?

问题描述

假设我有以下Haskell代码:

Let's say I have this Haskell code:

data RigidBody = RigidBody Vector3 Vector3 Float Shape -- position, velocity, mass and shape
data Shape = Ball Float -- radius
           | ConvexPolygon [Triangle]

用C ++表示这一点的最佳方法是什么?

What would be the best way to express this in C++?

struct Rigid_body {
    glm::vec3 position;
    glm::vec3 velocity;
    float mass;
    *???* shape;
};

我要问的是，当结构可以是两种类型之一时，如何在结构中表示形状.

The thing I'm asking is how to represent shape inside the struct when it can be one of two types.

推荐答案

在C ++中可以使用多种方法来解决该问题.

There are different approaches that can be used to solve that problem in C++.

纯OO方法将定义一个接口Shape，并具有两个不同的选项作为实现该接口的派生类型.然后，RigidBody将包含指向Shape的指针，该指针将被设置为引用Ball或ConvexPolygon.专业人士:人们喜欢OO(不确定这是否真的是专业人士:))，它很容易扩展(您以后可以添加更多形状而不更改类型).缺点:您应该为Shape定义一个适当的接口，它需要动态分配内存.

The pure-OO approach you would define an interface Shape and have the two different options as derived types implementing that interface. Then the RigidBody would contain a pointer to a Shape that would be set to refer to either a Ball or a ConvexPolygon. Pro: people love OO (not sure this is a pro really :)), it is easily extensible (you can add more shapes later on without changing the type). Con: You should define a proper interface for Shape, it requires dynamic allocation of memory.

放在OO之外，可以使用boost::variant或类似类型，它基本上是一个标记的联合，将容纳其中一种类型.优点:没有动态分配，形状是对象的局部.缺点:不是纯粹的OO(人们喜欢OO，您还记得吗?)，扩展起来不太容易，不能一般地使用形状

Putting OO aside, you can use a boost::variant or similar type, that is basically a tagged union that will hold one of the types. Pro: no dynamic allocations, shape is local to the object. Con: not pure-OO (people love OO, you remember right?), not so easy to extend, cannot use the shape generically

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