C++ - generic var manager

int main()
{
    VarManager vm;
    vm.AddVar("int", 0);
    vm.AddVar("float", 0.5f);
    vm.AddVar("string", std::string("test"));
 
    auto &v = static_cast<Var<int>&>(vm.GetVar("int"));
    int i = v.GetValue(); //0
 
    std::stringstream line("int 4");
    vm.ProcessCmd(line);
 
    i = v.GetValue(); //4
 
    return 0;
}

class BaseVar
{
public:
	BaseVar(std::string name)
		: _name(std::move(name))
	{
 
	}
	virtual ~BaseVar() = default;
 
	const std::string& GetName() const
	{
		return _name;
	}
 
	virtual bool ReadFromStream(std::istream &is) = 0;
 
private:
	std::string _name;
};
 
template<typename T>
class Var : public BaseVar
{
public:
	Var(std::string name, T &&value)
		: BaseVar(std::move(name)),
		_value(std::move(value))
	{
 
	}
 
	void SetValue(const T &value)
	{
		_value = value;
	}
 
	const T& GetValue() const
	{
		return _value;
	}
 
	virtual bool ReadFromStream(std::istream &is) override
	{
		is >> _value;
		return (bool)is;
	}
 
private:
	T _value;
};
 
class VarManager
{
public:
	template<typename T>
	void AddVar(const std::string &name, T &&value)
	{
		if (_vars.find(name) != std::end(_vars))
		{
			throw;
		}
 
		_vars[name] = std::make_unique<Var<T>>(std::move(name), std::forward<T>(value));
	}
 
	BaseVar& GetVar(const std::string &name)
	{
		return *_vars.at(name);
	}
 
	bool ProcessCmd(std::istream &is)
	{
		std::string name;
		if (!(is >> name))
		{
			return false;
		}
 
		auto it = _vars.find(name);
		if (it == std::end(_vars))
		{
			return false;
		}
 
		return it->second->ReadFromStream(is);
	}
 
private:
	std::unordered_map<std::string, std::unique_ptr<BaseVar>> _vars;
};