通过std :: function传递成员函数 [英] Passing a member function via std::function

问题描述

我要检查数据字段是否有效（有效表示不为null且未填充默认值）

I want to check if a data field is valid (valid means being not null and not filled with the default value)

基本上

return (!connector->IsNull(field_id) and connector->Get<type>Default(field_id, default_value))

但是类型可以是许多类型之一（字符串，int64等），因此有5-6种不同功能。我为此创建了一个辅助函数，并且尝试传递相关的GetDefault ...

But "type" can be one of many types (string, int64, etc...) so there are 5-6 different functions. I made a helper function for it and I'm trying to pass in the relevant GetDefault...

template<typename T> bool IsValidField(std::unique_ptr<Connector>& connector, const std::function<T(int, T)> &GetDefault, int field_id, T default_value){
  return (!connector->IsNull(field_id) && connection->GetDefault(field_id, default_value) != default_value);
}

然后我用...来调用辅助函数。

And I'm calling the helper function with....

IsValidField(connector, connector->GetStringWithDefault,20,"")

我得到错误错误：对非静态成员函数的引用必须称为
，因为GetStringWithDefault不是静态函数，我该如何解决？

I get the error "error: reference to non-static member function must be called " because GetStringWithDefault isnt a static function, how do I fix this?

或者，有没有办法使它显得不太尴尬？

Alternately, is there a way of making it slightly less awkward?

推荐答案

也许不是最整洁的，但是最简单的解决方案似乎是将所有内容包装到lambda中：

Perhaps not the most neat, but the most trivial solution seems to be to wrap everything into lambda:

IsValidField（connector，[connector ]（）-> T {return connector-> GetStringWithDefault（20，）}）

但是您需要进行调整 IsValidField 签名相应。

But then you need to adjust the IsValidField signature accordingly.

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