From: pjb@... (Pascal J. Bourguignon)
Date: 2009-07-22T00:05:10+09:00
Subject: Re: Best practice question: logging

Pito Salas <rps@salas.com> writes:

> I want to sprinkle my code (Ruby, not Rails) liberally with logging
> calls so that when things go wrong I can see what happened.
> [...]
> Any other tips or pointers would be greatly appreciated!

Ok, directly in the category "other tips", if you want to see
precisely what's happening, during debugging, you could "trace" the
methods.

I don't know if the feature is already implemented in Ruby, but it
should be possible to do so without too much difficulty.  

Basically, you would say:

   trace YourClass,:aMethod

and then the method YourClass.aMethod would be modified to print
tracing logs upon entering (with parameters), and exiting (with
results).

Tracing several methods would let you get logs such as:

C/USER[134]> (e 5)
 1. Trace: (E '5)
  2. Trace: (O '4)
   3. Trace: (E '3)
    4. Trace: (O '2)
     5. Trace: (E '1)
      6. Trace: (O '0)
      6. Trace: O ==> NIL
     5. Trace: E ==> NIL
    4. Trace: O ==> NIL
   3. Trace: E ==> NIL
  2. Trace: O ==> NIL
 1. Trace: E ==> NIL
NIL
C/USER[135]> (e 4)
 1. Trace: (E '4)
  2. Trace: (O '3)
   3. Trace: (E '2)
    4. Trace: (O '1)
     5. Trace: (E '0)
     5. Trace: E ==> T
    4. Trace: O ==> T
   3. Trace: E ==> T
  2. Trace: O ==> T
 1. Trace: E ==> T
T
C/USER[136]> 


When done, it would be useful to unwrap the methods with calls such as:

   untrace YourClass,:aMethod


-- 
__Pascal Bourguignon__