关于强类型枚举前向声明

发布于 2024-12-08 20:06:20 字数 947 浏览 0 评论 0原文

我的命名空间中有一组类，并且希望将前向声明分组到 Define.hpp 文件中。

我已经在其他项目中实现了这一点，这是一个示例：

namespace Makefile
{
    class Builder;
    class Config;
    class Options;
    class Target;
    class Tool;
}

我的问题是 - 例如 - Config 类包含以下强类型枚举：

namespace Makefile
{
    class Config
    {   
    public:
    enum class OperatingSystem : unsigned int 
        {   
            MacOSX = 0,
            Linux = 1,
            Windows = 2 
        };  
    };
}

所以我想在我的前向声明文件中添加此枚举类，并且添加以下行：

enum class Config::OperatingSystem : unsigned int;

我的问题来了，编译时出现以下错误：

src/Makefile/define.hpp:6:13: error: opaque-enum-specifier must use a simple identifier

这是否意味着无法前向声明嵌套类型？这个问题有什么解决办法吗？这是由于我的编译器造成的吗？

我的配置：Mac OS X.7 上的 GCC 4.6.0

编译标志：--std=c++0x -g3 -gdwarf-2 -W -Wall -iquote gen -iquote src

原文

I've a set of classes in my namespace and want to group forward declaration in a define.hpp file.

I've already achieve this in others projects, here is an example :

namespace Makefile
{
    class Builder;
    class Config;
    class Options;
    class Target;
    class Tool;
}

My problem is that — for example — the Config class include the following strongly typed enum :

namespace Makefile
{
    class Config
    {   
    public:
    enum class OperatingSystem : unsigned int 
        {   
            MacOSX = 0,
            Linux = 1,
            Windows = 2 
        };  
    };
}

So I would like to add this enum class in my forward-declaration file, and add the following line :

enum class Config::OperatingSystem : unsigned int;

Here comes my problem, I get the following error when compiling :

src/Makefile/define.hpp:6:13: error: opaque-enum-specifier must use a simple identifier

Does it mean that it is not possible to forward-declare nested type?
Is there any workaround to this problem?
Is this due to my compiler?

My configuration : GCC 4.6.0 on Mac OS X.7

Compilation flags : --std=c++0x -g3 -gdwarf-2 -W -Wall -iquote gen -iquote src

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不顾 2024-12-15 20:06:20

您只需在通常的位置创建不透明枚举即可：

namespace Makefile
{
    class Config
    {   
    public:
    enum class OperatingSystem : unsigned int;
    };
}

然后，无论您想要在何处定义枚举常量：

namespace Makefile
{
    enum Config::OperatingSystem : unsigned int
    {   
        MacOSX = 0,
        Linux = 1,
        Windows = 2 
    };
}

错误opaque-enum-specifier must use a simple identifier就是告诉您，如果您需要用简单标识符以外的方式引用枚举，你做错了。

更新：
根据您的特定需求，您可以简单地在类外部声明枚举，或者在仅包含不透明枚举的简单类中声明枚举，并从中继承 Config ：

namespace Makefile
{
    class ConfigDecl
    {
     public:
        enum class OperatingSystem : unsigned int;
    };
    class Config : public ConfigDecl;
}

You simply make the opaque enum in the usual place:

namespace Makefile
{
    class Config
    {   
    public:
    enum class OperatingSystem : unsigned int;
    };
}

And then, wherever you want to define the enum constants:

namespace Makefile
{
    enum Config::OperatingSystem : unsigned int
    {   
        MacOSX = 0,
        Linux = 1,
        Windows = 2 
    };
}

The error opaque-enum-specifier must use a simple identifier is there to tell you that if you need to refer to the enum with other than a simple identifier, you are doing it wrong.

UPDATE:
For your specific needs, you may simply declare the enum outside of the class, or else in a simple class with only the opaque enum, and inherit Config from it:

namespace Makefile
{
    class ConfigDecl
    {
     public:
        enum class OperatingSystem : unsigned int;
    };
    class Config : public ConfigDecl;
}

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