您应该在类的内部还是外部声明枚举? [英] Should you declare enums inside or outside a class?

问题描述

如果仅在类成员函数中使用枚举，应该在类的内部还是外部声明枚举?

namespace nspace
{

// need to append OC, as this pollutes the current namespace
enum OUTSIDE_CLASS {OC_POINTS, OC_LINES, OC_LINE_LOOP, :::};
enum OTHER_ENUM {OE_POINTS};
class VertexBuffer
{
public:
    enum INSIDE_CLASS {POINTS, LINES, LINE_LOOP, :::};
    void foo(OUTSIDE_CLASS e);
    void bar(INSIDE_CLASS e);
}
};

// usage
nspace::VertexBuffer v;
v.foo(nspae::VB_POINTS);
v.bar(nspace::VertexBuffer::POINTS); // more pedantic

解决方案

真正的目标是避免污染范围(全局或命名空间)，并帮助将相关值组合在一起(在IDE中使用自动补全实现漂亮的商品).

对于C ++ 11，您可以使用以下方法声明强类型的枚举:

enum class MyEnum {
  Value0,
  Value1
};

，必须以MyEnum::Value0(而不是Value0)调用.

在C ++ 03中，您可以通过以下方式或多或少地对此进行仿真:

struct MyEnum {
  enum Type {
    Value0,
    Value1
  };
};

但是，枚举的类型是MyEnum::Type，这是完全不同的.

懒惰的选择是将其转储到一个类中，但是我仍然赞成嵌套一个有作用域的枚举，即使是在一个类中，也只是为了清楚地表明这些值不是 loose 而是相互关联.

Should you declare enums inside or outside a class if the said enums are only used in the class member functions?

namespace nspace
{

// need to append OC, as this pollutes the current namespace
enum OUTSIDE_CLASS {OC_POINTS, OC_LINES, OC_LINE_LOOP, :::};
enum OTHER_ENUM {OE_POINTS};
class VertexBuffer
{
public:
    enum INSIDE_CLASS {POINTS, LINES, LINE_LOOP, :::};
    void foo(OUTSIDE_CLASS e);
    void bar(INSIDE_CLASS e);
}
};

// usage
nspace::VertexBuffer v;
v.foo(nspae::VB_POINTS);
v.bar(nspace::VertexBuffer::POINTS); // more pedantic

解决方案

The real goal is to avoid polluting the scope (either global or namespace) and help grouping related values together (works pretty goods with autocompletion in IDE).

With C++11, you can declare strongly typed enums using:

enum class MyEnum {
  Value0,
  Value1
};

which are necessarily invoked as MyEnum::Value0 (and not Value0).

In C++03, you can more or less emulate this with:

struct MyEnum {
  enum Type {
    Value0,
    Value1
  };
};

But then the type of the enum is MyEnum::Type which is subtly different.

The lazy option is to just dump it in a class, but I still favor nesting a scoped enum, even within a class, just to make it clear that those values are not loose but instead are inter-related.

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