From: Matju <matju@...>
Date: 2004-11-12T04:59:05+09:00
Subject: Re: Converting nil to NULL


On Fri, 12 Nov 2004, Berger, Daniel wrote:

> I asked this on ruby-talk, but I thought I should ask here as well.
> I find I'm often doing something like this:
> static VALUE foofoo(int argc, VALUE* argv, VALUE self)
>    char* foo;
>    VALUE rbFoo;
>    rb_scan_args(argc,argv,"01",&rbFoo);
>    if(NIL_P(rbFoo)){
>       foo = NULL;
>    }
>    else{
>       foo = StringValuePtr(rbFoo);
>    }
> Is there a way to reduce this to a single step?  Can we modify
> StringValuePtr() to return NULL if its argument is nil?  Or would that
> break too many things?

In addition to Charles' solution, which is good, I'd like to say that the
conditional expressions of C are not evil. You can write:

foo = NIL_P(rbFoo) ? NULL : StringValuePtr(rbFoo);

and it _wouldn't_ be a crime and it wouldn't make little Jesus cry.

After all, Ruby has _eight_ different kinds of conditional expressions
(the ?: syntax, the if/end syntax, and the
"&&"/"||"/"and"/"or"/"if"/"unless" binary operators), which is slightly
more than in PERL. I don't mean it's right to have so many options
syntax-wise, but rather that if there are so many, then it's surely not
considered evil in the Ruby culture. This kind of relativity prompts to
reconsider the rule in the C culture.

If you follow a certain coding standard that forbids conditional
expressions, let me tell you, the purpose of a coding standard is to make
things smoother, and not cumbersome.

All that said, it's still better to make a function or macro out of this,
especially if you do it very often.

In my biggest C++ program I go as far as... well... just imagine what it
would like if rb_scan_args had a full, user-extensible type conversion
system. THEN you can cut down a _lot_ on code, as you wouldn't even have
to call StringValuePtr directly, neither your own NULL-savvy wrapper.
Preserves the brain for the more challenging aspects of programming.

_____________________________________________________________________
Mathieu Bouchard -=- Montr�al QC Canada -=- http://artengine.ca/matju