c++ - 此代码是否违反一个定义规则？

Question

AOSP10中的某些代码似乎违反了ODR:

来源1:

struct ExtentsParam
{
  void init (const OT::cff1::accelerator_t *_cff)
  {
    path_open = false;
    cff = _cff;
    bounds.init ();
  }
  void start_path ()         { path_open = true; }
  void end_path ()           { path_open = false; }
  bool is_path_open () const { return path_open; }
  bool    path_open;
  Bounds  bounds;
  const OT::cff1::accelerator_t *cff;
};

从:
https://android.googlesource.com/platform/external/harfbuzz_ng/+/refs/heads/android10-gsi/src/hb-ot-cff1-table.cc

来源2:

struct ExtentsParam
{
  void init ()
  {
    path_open = false;
    min_x.set_int (0x7FFFFFFF);
    min_y.set_int (0x7FFFFFFF);
    max_x.set_int (-0x80000000);
    max_y.set_int (-0x80000000);
  }
  void start_path ()         { path_open = true; }
  void end_path ()           { path_open = false; }
  bool is_path_open () const { return path_open; }
  void update_bounds (const Point &pt)
  {
    if (pt.x < min_x) min_x = pt.x;
    if (pt.x > max_x) max_x = pt.x;
    if (pt.y < min_y) min_y = pt.y;
    if (pt.y > max_y) max_y = pt.y;
  }
  bool  path_open;
  Number min_x;
  Number min_y;
  Number max_x;
  Number max_y;
};

从:
https://android.googlesource.com/platform/external/harfbuzz_ng/+/refs/heads/android10-gsi/src/hb-ot-cff2-table.cc

构建脚本:

...
srcs: [
    ...
    "src/hb-ot-cff1-table.cc",
    "src/hb-ot-cff2-table.cc",
],
...

https://android.googlesource.com/platform/external/harfbuzz_ng/+/refs/heads/android10-gsi/Android.bp

这些资源也内置在同一共享库中。两种来源都有“struct ExtentsParam”的定义，内容绝对不同。这两个结构似乎仅在本地使用。

这两个来源具有相似的名称，因此，非故意的名称重复的机会很小。而且Google违反ODR的机会可能很小。

可以？

Answer 1

是:因为它们都在全局 namespace 中，所以这绝对违反了ODR。

只有在定义它们的翻译单元内使用的类类型才有豁免。一个程序只能包含一个具有任何给定名称的类类型。

它是满足免除此规则的标准的第一个要求:

There can be more than one definition of a [..] class type [..] in a program provided that each definition appears in a different translation unit, and provided the definitions satisfy the following requirements. [..] Given such an entity named D defined in more than one translation unit, all of the following requirements shall be satisfied. [..] Each definition of D shall consist of the same sequence of tokens [..] (ref)

开发人员只是“很幸运”，链接器没有尝试做任何导致这种违规症状的滑稽 Action 。

这就是 namespace 的用途。例如，如果类类型仅在定义它的转换单元中使用，则它可能已经在匿名 namespace 中定义了。