From: Bill Kelly <billk@...>
Date: 2003-12-30T07:16:44+09:00
Subject: Re: Question about Ruby implementation

Hi,

From: "Jamis Buck" <jgb3@email.byu.edu>
>
> [...] I have a question now about some of 
> the macros I've seen:  why do some macros wrap their contents in a "do { 
> ... } while(0)"?  Is this preferable to simply wrapping them in curly 
> braces ("{...}")?  Is it simply a matter of matz's programming style, or 
> is there some subtler issue in effect here?

It's a 'C' language idiom.  It makes a terminating semi-colon
a required part of the syntax, which helps avoid mistakes
with the one-liner form of (for instance) if/else statements,
and such.

#define THING1 {blah()}
#define THING2 do{blah()}while(0)

if (rand() & 1)
  THING1();
else  
  THING2();

...note problem with THING1() usage, given the extraneous
semi-colon...


HTH,

Regards,

Bill