在C ++中，如何制作一个可以包含相同变体向量的变体？ [英] In C++, how to make a variant that can contain a vector of of same variant?

问题描述

我试图制作一个std :: variant，它可以包含相同变体的向量：

  class ScriptParameter; 
使用ScriptParameter = std :: variant< bool，int，double，std :: string，std :: vector< ScriptParameter> > ;; 
  

我正在重新定义ScriptParameter。

有没有办法实现也可以包含相同类型变量的数组的变量？

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解决方案

由于前向声明说 ScriptParameter 是一个类，因此您不能使用使用别名。但是，这里并没有什么内在的错误，因为 vector 只是一个指针，所以没有真正的循环依赖。

您可以使用继承：

  class ScriptParameter; 
类ScriptParameter 
：公共std :: variant< bool，int，double，std :: string，std :: vector< ScriptParameter> > 
 {
 public：
使用base = std :: variant< bool，int，double，std :: string，std :: vector< ScriptParameter> > ;; 
使用base :: base; 
使用base :: operator =; 
}; 
 
 int main（）{
 ScriptParameter sp { hello}; 
 sp = 1.0; 
 std :: vector< ScriptParameter> vec; 
 sp = vec; 
 std :: cout<< sp.index（）<<  \n; 
} 
  

I a trying to make a std::variant that can contain a vector of the same variant:

class ScriptParameter;
using ScriptParameter = std::variant<bool, int, double, std::string, std::vector<ScriptParameter> >;

I am getting ScriptParameter redefinition. It think it is possibly because a template parameter cannot be forward declared?

Is there a way to achieve a variant that could also contain an array of same typed variants?

解决方案

Since the forward declaration says ScriptParameter is a class, you can't use using alias. However, nothing is inherently wrong here, since vector is only a pointer, there is no real circular dependency.

You can use inheritance:

class ScriptParameter;
class ScriptParameter
    : public std::variant<bool, int, double, std::string, std::vector<ScriptParameter> >
{
public:
    using base = std::variant<bool, int, double, std::string, std::vector<ScriptParameter> >;
    using base::base;
    using base::operator=;
};

int main() {    
    ScriptParameter sp{"hello"};
    sp = 1.0;
    std::vector<ScriptParameter> vec;
    sp = vec;    
    std::cout << sp.index() << "\n";  
}

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