From: Gerald <gerr41@...>
Date: 2006-07-29T17:00:15+09:00
Subject: What method should a class provide for printf's %c format string ?


Consider the following snippet:

---------------------------------------------

#!/usr/bin/ruby

class Thing
           
        def initialize(name)
                @name = name
        end
           
        def to_s
                @name
        end
           
        def to_i
                @name.length
        end
end

a = Bla.new("foo")

printf "%s\n", a
printf "%d\n", a
printf "%c\n", a

---------------------------------------------

This code breaks at the last line with the message :

./go7:22:in `printf': can't convert Thing into Integer (TypeError)

It seems that the printf conversion to %c tries to call a specific
method of my class to convert the object to the appropriate format. I am
a bit confused about the message "can't convert to integer", since the
to_i method is defined, and sucessfully called that the printf "%d"
line.

So, two questions arise

- what method am I supposed to provied for printf so it can handle the
  '%s' format string

- How can I figure this out myself. It seems that printf is trying to
  call something, but I have no way of telling exactly  what  it is
  trying to do. Is there some kind of tracing/debugging that can be
  switched on to see what's printf is trying to do ?

Thank you very much,