Inifinity recursion && test/unit

ruby-talk
1

Without test/unit ruby finished work and said that stack level too deep.
Is this correct that in this code ruby goes to infinity recursion?

ruby 1.8.0 (2003-06-06) [i386-freebsd4.7]

···

#!/usr/local/bin/ruby
require ‘test/unit’

module Recur
def self.new
Recur.new
end
end

class Tests < Test::Unit::TestCase
def test_1
Recur.new
end
end

–
with best regards,
Andrey Kulinich
IT Group
Software developer
phone/fax +380 (372) 58-43-10
e-mail: Andrey.Kulinich@itgrp.net
http://www.itgrp.net

2

Yep, that’s definitely a nice piece of infinite recursion. What are you
trying to achieve?

module Recur
def self.new ==> same as def Recur.new

Regards,

Brian.

···

On Tue, Jul 01, 2003 at 05:34:06PM +0900, Andrey Kulinich wrote:

Without test/unit ruby finished work and said that stack level too deep.
Is this correct that in this code ruby goes to infinity recursion?

ruby 1.8.0 (2003-06-06) [i386-freebsd4.7]

#!/usr/local/bin/ruby
require ‘test/unit’

module Recur
def self.new
Recur.new
end
end

class Tests < Test::Unit::TestCase
def test_1
Recur.new
end
end

3

Brian Candler wrote:

#!/usr/local/bin/ruby
require ‘test/unit’

module Recur
def self.new
Recur.new
end
end

class Tests < Test::Unit::TestCase
def test_1
Recur.new
end
end
Yep, that’s definitely a nice piece of infinite recursion. What are you
trying to achieve?

Originally that was an error. Code:

···

module Recur
def self.new
Recur.new
end

 class Recur
 end

end

Recur.new

But after that I rename class Recur to Another and forgot to change in
def self.new.
Without test/unit ruby said that there is an infinite recursion. Is that
a bug or a feature?

module Recur
def self.new ==> same as def Recur.new

Almost. Depends on position of definition.

–
with best regards,
Andrey Kulinich
IT Group
Software developer
phone/fax +380 (372) 58-43-10
e-mail: Andrey.Kulinich@itgrp.net
http://www.itgrp.net

4

Originally that was an error. Code:

module Recur
def self.new
Recur.new
end

 class Recur
 end

end

Recur.new

OK, so you have defined:

  • a module Recur
  • a class Recur::Recur
  • a module function Recur::new which calls Recur::Recur.new
    (it looks in its own namespace before trying enclosing namespaces,
    so Recur::Recur.new is used if it exists; if it doesn’t then it will
    find Recur.new in the top-level namespace)

So this is not recursive.

But after that I rename class Recur to Another and forgot to change in
def self.new.
Without test/unit ruby said that there is an infinite recursion. Is that
a bug or a feature?

Neither, it’s correct behaviour. If class Recur no longer exists, then the
call to ‘Recur.new’ will refer to the function ‘new’ in module Recur, which
is itself (hence infinitely recursive).

Regards,

Brian.

···

On Tue, Jul 01, 2003 at 08:38:42PM +0900, Andrey Kulinich wrote:

5

Brian Candler wrote:

But after that I rename class Recur to Another and forgot to change in
def self.new.
Without test/unit ruby said that there is an infinite recursion. Is that
a bug or a feature?
Neither, it’s correct behaviour. If class Recur no longer exists, then the
call to ‘Recur.new’ will refer to the function ‘new’ in module Recur, which
is itself (hence infinitely recursive).

I was talking about test/unit.
Why when I’m using it in such code ruby can’t detect infinite loop? In
my opinion this is test/unit’s bug.

···

–
with best regards,
Andrey Kulinich
IT Group
Software developer
phone/fax +380 (372) 58-43-10
e-mail: Andrey.Kulinich@itgrp.net
http://www.itgrp.net

6

I don’t think Ruby really “detects” infinite loops; it simply runs out of
memory and reports it.

When I run your code from RubyTalk:74829 I get:

$ ruby x.rb 2>&1 | head -20
Loaded suite x
Started
…
Error!!!
test_1(Tests):
SystemStackError: stack level too deep
x.rb:6:in new' x.rb:6:in new’
x.rb:6:in new' x.rb:6:in new’
x.rb:6:in new' x.rb:6:in new’
… etc

Now if I strip out the test/unit stuff I get almost exactly the same error:

$ cat x.rb
#!/usr/local/bin/ruby
module Recur
def self.new
Recur.new
end
end

Recur.new

$ ruby x.rb 2>&1
x.rb:4:in New': stack level too deep (SystemStackError) from x.rb:4:in New’
from x.rb:4:in New' from x.rb:4:in New’
from x.rb:4:in New' from x.rb:4:in New’
from x.rb:4:in New' from x.rb:4:in New’
from x.rb:4:in New' ... 66668 levels... from x.rb:4:in New’
from x.rb:4:in New' from x.rb:4:in New’
from x.rb:8

The only difference seems to be that the error report has this optimisation
of “… 66668 levels…” in there (This is ruby-1.6.8, incidentally)

test/unit traps exceptions, so that
(a) it can count errors, and
(b) it can display errors in the appropriate place (you might be running
with a GTk testrunner, for example)

So I wouldn’t expect it to give exactly the same output as Ruby’s default
exception handler. It does seem pretty close to me though.

If you don’t think test/unit is doing the right thing, can you post the
output of running your test program under test/unit, the output when run
without test/unit, and how you think it should be changed?

Regards,

Brian.

···

On Tue, Jul 01, 2003 at 10:06:46PM +0900, Andrey Kulinich wrote:

I was talking about test/unit.
Why when I’m using it in such code ruby can’t detect infinite loop? In
my opinion this is test/unit’s bug.

7

Huh? What do you expect Test::Unit to do? Given this input, with
ruby-1.8.0-preview3 and whatever version of test/unit comes with that:

require ‘test/unit’

def recursive()
recursive()
end

class TC_recursive < Test::Unit::TestCase
def test_recursive
recursive()
end
end

…when run, will give this output:

Loaded suite recur
Started
E
Finished in 0.098239 seconds.

  1. Error!!!
    test_recursive(TC_recursive):
    SystemStackError: stack level too deep
    recur.rb:6:in recursive' recur.rb:6:in recursive’
    recur.rb:6:in recursive' recur.rb:6:in recursive’
    recur.rb:6:in recursive' <snipped several thousand lines of traceback> recur.rb:6:in recursive’
    recur.rb:6:in recursive' recur.rb:6:in recursive’
    recur.rb:6:in recursive' recur.rb:6:in recursive’
    recur.rb:6:in recursive' recur.rb:6:in recursive’
    recur.rb:11:in `test_recursive’
    recur.rb:10

1 tests, 0 assertions, 0 failures, 1 errors

What’s the problem?

Jason Creighton

···

On Tue, 1 Jul 2003 22:06:46 +0900 Andrey Kulinich Andrey.Kulinich@itgrp.net wrote:

Neither, it’s correct behaviour. If class Recur no longer exists, then the
call to ‘Recur.new’ will refer to the function ‘new’ in module Recur,
which is itself (hence infinitely recursive).

I was talking about test/unit.
Why when I’m using it in such code ruby can’t detect infinite loop? In
my opinion this is test/unit’s bug.

8

Andrey Kulinich Andrey.Kulinich@itgrp.net writes:

I was talking about test/unit.
Why when I’m using it in such code ruby can’t detect infinite loop? In
my opinion this is test/unit’s bug.

By definition, a program can’t detect whether it’ll exit or not
without actually running itself. It’s known as the Halting Problem,
and it’s a fundamental theorem of Computer Science.

-=Eric

···

–
Come to think of it, there are already a million monkeys on a million
typewriters, and Usenet is NOTHING like Shakespeare.
– Blair Houghton.

9

I’d guess so to–. Wouldn’t this be a “halting problem” issue? =)

···

On Tue, Jul 01, 2003 at 10:06:46PM +0900, Andrey Kulinich wrote:

I was talking about test/unit.
Why when I’m using it in such code ruby can’t detect infinite loop? In
my opinion this is test/unit’s bug.

I don’t think Ruby really “detects” infinite loops; it simply runs out of
memory and reports it.