专用类型的模板专业化 [英] Template Specialization for Private Types

问题描述

我有一个通用算法，需要访问其模板类型的特征.有一个特质类可以专门提供这些特质.

I have a generic algorithm that needs to access its template type's traits. There is a trait class that can be specialized for providing these traits.

在我的课程中使用此算法时，我想将其与课程中定义的私有类型一起使用.

When using this algorithm within my class, I'd like to use it with a private type defined within the class.

但是，专业化只能在无法访问我的类的 namespace 或全局范围内进行.

However, specialization can only happen within namespace or global scope where my class is inaccessible.

class A
{
    struct Secret 
    {};
};

template <typename T> struct Trait {};

// Inaccessible type ----vvvvvvvvv
template <> struct Trait<A::Secret> // Specialize for  PRIVATE type A::Secret
{ 
    A::Secret magic_value() { return{}; } // ERROR: 'A::Secret': cannot access private struct declared in class 'A'
};  

是否有可能以某种方式专门化具有私有类型的模板，至少在可访问该类型的范围内?

Is it possible to somehow specialize a template with a private type, at least in scopes where this type is accessible?

也许可以将专门化声明为 friend 类?

Maybe it's possible to declare the specialization a friend class?

推荐答案

您可以通过或参考 A :: Secret 的完整专业知识.

Or refer to the full specialization of A::Secret.

template <typename T> struct Trait {};
class A
{
    struct Secret 
    {};

    friend struct Trait<A::Secret>;
};

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