Re: [boost] [algorithm][hex] function hex_char_to_int in unnamed namespace in header file

Subject: Re: [boost] [algorithm][hex] function hex_char_to_int in unnamed namespace in header file
From: Felipe Magno de Almeida (felipe.m.almeida_at_[hidden])
Date: 2012-12-10 14:01:18

Ping?

On Mon, Dec 3, 2012 at 6:09 PM, Felipe Magno de Almeida
<felipe.m.almeida_at_[hidden]> wrote:
> On Mon, Dec 3, 2012 at 5:58 PM, Marshall Clow <mclow.lists_at_[hidden]> wrote:
>> On Dec 3, 2012, at 9:43 AM, Felipe Magno de Almeida <felipe.m.almeida_at_[hidden]> wrote:
>
> [snip]
>
>>> If any entity defined in a unnamed namespace is used in
>>> an external linkage definition, such as a
>>> inline function or a template definition and this definition is used
>>> in multiple TUs it causes ODR violations, because
>>> it is defined differently (uses different entities) in each TU.
>>
>> And No. Because the call to it (in each TU) will call the entity in the specific unnamed namespace that was part of that translation unit.
>
> Yes. The problem is not the call. Is that the definition of the inline
> function and/or template are different from each other. Because they
> refer to different functions in each TU. And that is a ODR violation.
>
> Let me try to illustrate:
>
> -- foo.h
> namespace {
> void foo() {}
> }
>
> -- bar.h
> #include "foo.h"
> template <typename T>
> void bar(T object)
> {
>   foo();
> }
>
> -- file1.cpp
> #include "bar.h"
>
> bar(5);
>
> -- file2.cpp
> #include "bar.h"
>
> bar(5);
>
> --
>
> The template bar is defined differently for file1.cpp and file2.cpp because each
> identifier do not represent the same entity. Which is a ODR violation, since
> their definitions must equal to each other. The same would apply just
> as well for
> an inline function.
>
>> My mental model for unnamed namespaces is "a namespace with a unique compiler-generated name"
>
> Yes, the same here. The problem is when a function,outside a unnamed
> namespace, uses something
> defined in a unnamed namespace, its definition can't be equal across
> multiple TUs anymore,
> because the namespace has a different "unique compiler-generated name".
>
>> -- Marshall
>>
>> Marshall Clow     Idio Software   <mailto:mclow.lists_at_[hidden]>
>>
>> A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait).
>>         -- Yu Suzuki
>
> Regards,
> --
> Felipe Magno de Almeida

-- 
Felipe Magno de Almeida