From: Christian Boos <cboos@...>
Date: 2002-04-19T06:03:19+09:00
Subject: RE: Confused by example in Pickaxe book

Hello,

You should have a look to the signature of those
methods. It's pretty simple:

> -----Original Message-----
> From: Daniel Berger [mailto:djberg96@hotmail.com]
> Sent: Thursday, April 18, 2002 5:47 PM
> To: ruby-talk ML
> Subject: Confused by example in Pickaxe book
> 
> 
> Hi all,
> 
> On p. 181 of the Pickaxe, the example defines the "initialize" method
> like this:
> 
> rb_define_method(cCDPlayer,"initialize",cd_init,1);
> 

... CDPlayer#initialize will take one fixed argument.

> Yet, in the "new" method it's called like this:
> 
> rb_obj_call_init(tdata,1,argv);
> 

This function uses a argc-argv style list of VALUEs.
'1' is the count of elements in the C array of VALUEs.
Internally, 'rb_obj_call_init' will use 'rb_funcall2' to call 
the "initialize" method on the 'tdata' object.

> First, isn't that 2 arguments instead of 1 (remembering to exclude
> 'self', i.e. tdata, as an argument).  What is the '1' for?
> 
> Second, what is the purpose of this?
> 
> VALUE argv[1];
> argv[0] = unit;
> 
> What is happening here?
> 

... when using 'rb_obj_call_init', one has to pack
the arguments in a C array of VALUEs, even if there's
only one argument.
I guess that in that specific case, one could write the call
in a shorter way:

 rb_obj_call_init(tdata,1,&unit);

... but this would be even more confusing :)

> Much confused.
> 

Hope it helps :)

> Regards,
> 
> Dan
> 
>