请考虑以下测试用例(从LLVM源减少(：
//% cat foo1.cpp
#include <memory>
namespace {
class A {
int i;
};
}
class G {
std::unique_ptr<A> foo() const;
};
std::unique_ptr<A> G::foo() const { return std::make_unique<A>(); }
和
//% cat foo2.cpp
#include <memory>
namespace {
class A {
bool a;
};
}
class H {
std::unique_ptr<A> bar() const;
};
std::unique_ptr<A> H::bar() const { return std::make_unique<A>(); }
这是否违反了一个定义规则？
gcc-6目前这样认为：
~ % g++ -flto -shared -std=c++14 foo1.cpp foo2.cpp
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:187:72: warning: type ‘struct _Base’ violates one definition rule [-Wodr]
typedef _Head_base<_Idx, _Head, __empty_not_final<_Head>::value> _Base;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:187:72: note: a different type is defined in another translation unit
typedef _Head_base<_Idx, _Head, __empty_not_final<_Head>::value> _Base;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:147:13: note: the first difference of corresponding definitions is field ‘_M_head_impl’
_Head _M_head_impl;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:147:13: note: a field of same name but different type is defined in another translation unit
_Head _M_head_impl;
^
foo1.cpp:3:7: note: type ‘struct A’ defined in anonymous namespace can not match type ‘struct A’
class A {
^
foo2.cpp:3:7: note: the incompatible type defined in anonymous namespace in another translation unit
class A {
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:598:40: warning: type ‘struct _Inherited’ violates one definition rule [-Wodr]
typedef _Tuple_impl<0, _T1, _T2> _Inherited;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:598:40: note: a type with the same name but different base type is defined in another translation unit
typedef _Tuple_impl<0, _T1, _T2> _Inherited;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:102:12: note: type ‘struct _Head_base’ defined in anonymous namespace can not match type ‘struct _Head_base’
struct _Head_base<_Idx, _Head, false>
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:102:12: note: the incompatible type defined in anonymous namespace in another translation unit
struct _Head_base<_Idx, _Head, false>
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/bits/unique_ptr.h:151:41: warning: type ‘struct element_type’ violates one definition rule [-Wodr]
typedef _Tp element_type;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/bits/unique_ptr.h:151:41: note: a different type is defined in another translation unit
typedef _Tp element_type;
^
foo1.cpp:4:7: note: the first difference of corresponding definitions is field ‘i’
int i;
^
foo2.cpp:4:8: note: a field with different name is defined in another translation unit
bool a;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:598:40: warning: type ‘struct _Inherited’ violates one definition rule [-Wodr]
typedef _Tuple_impl<0, _T1, _T2> _Inherited;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:598:40: note: a type with the same name but different base type is defined in another translation unit
typedef _Tuple_impl<0, _T1, _T2> _Inherited;
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:102:12: note: type ‘struct _Head_base’ defined in anonymous namespace can not match type ‘struct _Head_base’
struct _Head_base<_Idx, _Head, false>
^
/home/trippels/gcc_test/usr/local/include/c++/6.0.0/tuple:102:12: note: the incompatible type defined in anonymous namespace in another translation unit
struct _Head_base<_Idx, _Head, false>
^
这是GCC错误(在devel树中只出现了几天(。这个问题是由另一个修复程序引起的，该修复程序使GCC认为隐式typedefs是非匿名的，因此外部结构被类型合并(不正确地这样做(。测试用例现在已经修复，我很想听到更多可能看起来虚假的警告。
一个类有两种不同的定义。将两者编译在一起会导致直接冲突，除非这两者最终位于不同的命名空间中。我想这可能是对的。
您可能想要查找的是这两个实现特性是否互斥。可能有两个不同的源文件具有不同的定义，但在某些情况下，具有两个定义可能是有意义的(即，我在Windows和Linux上有一个线程API，我需要基于我的编译设置具有两个不同定义(。