From: Michael Widenius
Date: June 24 2009 3:04pm
Subject: Re: MySql coding style: Request for deprecation of UPPERCASE typedefs
List-Archive: http://lists.mysql.com/internals/36986
Message-Id: <19010.16495.278406.999506@narttu.askmonty.org>
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Hi!

>>>>> "Mats" == Mats Kindahl <Mats.Kindahl@stripped> writes:

Mats> Tor Didriksen wrote:
>> hi
>> 
>> "Structure types are typedef'ed to an all-upper-case identifier."
>> Can someone explain the reasoning behind this?
>> ALL_UPPERCASE_NAME says DANGEROUS_THIS_IS_A_MACRO to me, rather than
>> struct/class.
>> 
>> typedef struct foo { ... } FOO;
>> Is legacy C-style, and does not belong in a C++ style guide (imho).

Mats> I agree.

Mats> In addition, it is a problem because there cannot be multiple typedefs, but
Mats> there can be multiple forward declarations, which makes it very difficult to do
Mats> a forward declaration of a structure using, e.g.:

Mats> typedef struct foo FOO;

Mats> In the event that the header file is included by some other file that does a
Mats> similar forward declaration, the compiler will throw an error.

We have already solved this in many places of MySQL / mysys by using struct
foo for cases where the typedef is not yet done so I wouldn't call
this a notable problem.

I also tested this with gcc and didn't get any error for the
following file:

typedef struct foo FOO;
struct foo {int a;};
typedef struct foo FOO;

struct foo a;
FOO b;

What is it that would give an error?

Mats> I would prefer if we never used typedef to introduce aliases for
Mats> struct/class/union, they cause more problem that it's worth, and they are not
Mats> needed in C++ at all.

MySQL was coded in part so that it would be able to easily mix C++ and
C code and allow you to move things from C++ and C with little work.

As MySQL is using C libraries with typedefs, you can't easily get rid
of all the typedefs.

Regards,
Monty