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Subject: Re: [boost] [filesystem] Version 3 request for comments
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2009-02-11 11:18:44
----- Original Message -----
From: "Beman Dawes" <bdawes_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Wednesday, February 11, 2009 4:50 PM
Subject: Re: [boost] [filesystem] Version 3 request for comments
> In C++0x, the preferred practice for such constants is probably going
> to be to use a scoped enum:
>
> enum class file_type
> {
> status_unknown,
> file_not_found,
> regular,
> directory,
> symlink,
> block,
> character,
> fifo,
> socket,
> type_unknown
> };
>
> That's a lot more satisfying. We can emulate that approach in C++03 like this:
>
> #ifndef BOOST_NO_SCOPED_ENUM
>
> enum class file_type
> {
> status_unknown,
> file_not_found,
> regular,
> directory,
> symlink,
> block,
> character,
> fifo,
> socket,
> type_unknown
> };
>
> typedef file_type file_type_enum;
>
> #else
> namespace file_type
> {
> enum types
> {
> status_unknown,
> file_not_found,
> regular,
> directory,
> symlink,
> block,
> character,
> fifo,
> socket,
> type_unknown
> };
> }
>
> typedef file_type::types file_type_enum;
> #endif
>
> Is such a scoped enum approach worth taking?
>
> I haven't made up my mind; I'd like to think about it for a few days
> and also see what could be done to preserve existing code.
Hi,
the question is how the user will use these enumerations. if BOOST_NO_SCOPED_ENUM is not defined the user can write
file_type e = file_type::file_not_found;
which will not evidently compile when defined. How can we force the user to write
file_type_enum e = file_type::file_not_found;
which is not intuitive, i.e. there is no explicit relation between file_type_enum and file_type. What about making this relation explicit using a metafunction?
I'm don't know if the following is clearer
enumeration<file_type>::type e = file_type::file_not_found;
Best,
Vicente
__________________________________
#ifndef BOOST_NO_SCOPED_ENUM
template <typename E>
struct enummeration {
typedef E type;
};
#else
template <typename E>
struct enummeration {
typedef E::type type;
};
#endif
#ifndef BOOST_NO_SCOPED_ENUM
enum class file_type
{
status_unknown,
file_not_found,
regular,
directory,
symlink,
block,
character,
fifo,
socket,
type_unknown
};
typedef file_type file_type_enum;
#else
struct file_type
{
enum type
{
status_unknown,
file_not_found,
regular,
directory,
symlink,
block,
character,
fifo,
socket,
type_unknown
};
}
typedef file_type::types file_type_enum;
#endif
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