Hello,
I’m working with a third-party library that calls both putc and puts
in a certain method. I’d like to discard what is written with putc
for the duration of the method while keeping anything written to
puts. Given that the method lets you hook in your own code at its
start and end, how do I do this?
I’ve tried various approaches including replacing $stdout with a
custom class, and opening $stdout and rewriting putc – but I haven’t
quite succeeded.
For example, here’s some code that doesn’t work:
class << $stdout
alias :original_putc :putc
def putc(obj)
end
end
putc ‘b’
=> “b” # I was hoping for no output
And some more non-working code:
class MyIO < StringIO
def putc(obj)
end
end
In hook called at start of target method
$original_stdout = $stdout
$stdout = MyIO.new
In hook called at end of target method
$stdout = $original_stdout
Result: both putc and puts appear to be discarded.
Could anyone please show me the light?
Thanks in advance,
Andy S.
Lars T. wrote:
What about
def putc(obj)
end
puts “Hello”
putc “W”
Did I miss something?
Yep, switching it back to normal.
Andrew S. wrote:
Could anyone please show me the light?
Try this:
putc 65
puts 65
def func
alias orig_putc putc
def putc(*args)
end
putc 66
puts 66
alias putc orig_putc
end
func
putc 67
puts 67
–output:–
A65
66
C67
7stud – wrote:
def putc(*args)
end
Hmmm…I guess you don’t need the *args–apparently putc can only take
one arg.
On 2 Oct 2007, at 13:36, 7stud – wrote:
alias putc orig_putc
end
Aliasing back again worked – thanks.
It produces a warning (“discarding old putc”) when it encounters the
second alias, at the end of the target method. But I can live with
that. Maybe undefining putc first would stop the warning but it’s
not immediately obvious to me how to do that.
Thanks for your help. I greatly appreciate it.
Regards,
Andy S.
Hi,
On Tue, 2007-10-02 at 20:02 +0900, Andrew S. wrote:
putc ‘b’
=> “b” # I was hoping for no output
Since I think other people satisfactorily answered the rest, note here
that “b” is a return value, and that a normal putc would look like this
on a console:
irb(main):001:0> putc ‘b’
b=> “b”
irb(main):002:0>
So it was successful here. 
Arlen
On Oct 2, 2007, at 7:02 AM, Andrew S. wrote:
For example, here’s some code that doesn’t work:
Could anyone please show me the light?
Running the following code may cast some light on your problem.
class << $stdout
def putc(obj)
puts "1 called"
end
end
class << STDOUT
def putc(obj)
puts "2 called"
end
end
module Kernel
def putc(obj)
puts "3 called"
end
end
putc ‘b’
Regards, Morton
On 2 Oct 2007, at 14:29, Morton G. wrote:
puts "2 called"
end
end
module Kernel
def putc(obj)
puts “3 called”
end
end
putc ‘b’
Thanks, Morton, that’s a good, methodical way to determine what’s
being called. Most helpful.
Regards,
Andy S.
Andrew S. wrote:
On 2 Oct 2007, at 13:36, 7stud – wrote:
alias putc orig_putc
end
Aliasing back again worked – thanks.
It produces a warning (“discarding old putc”) when it encounters the
second alias, at the end of the target method. But I can live with
that.
I think the warning is saying, "Hey, there won’t be any reference to the
putc def inside func if you do that last alias. Well, how about using
another alias to save the putc def in?
…
alias garbage putc
alias putc orig_putc
end
On 2 Oct 2007, at 16:54, 7stud – wrote:
that.
end
Ah, I see. Adding another alias does indeed obviate the warning.
Thanks for the insight.
Regards,
Andy S.
