Redefine while

Ruby
1

Hi, is there an easy way to redefine ‘while’. I have a class that uses a
while loop. In my unit test it always evaluates to false (which is
correct). I only want the loop to run once, and the enter. Just like an
if.

This is the code I’ve tried:

def while(condition)
p “redefined while!”
yield if condition
end

while true do
p “hello”
sleep 1
end

But it loops eternally.
Any help?

2

On Thu, Nov 6, 2008 at 10:00 AM, Emil S. [email protected] wrote:

yield if condition
end

while true do
p “hello”
sleep 1
end

But it loops eternally.
Any help?
The problem is that while is not a method in ruby but a keyword
[reserved word].

Michael G.

3

On Thu, Nov 6, 2008 at 10:00 AM, Emil S. [email protected] wrote:

yield if condition

Posted via http://www.ruby-forum.com/.

Not possible. ‘while’ is a keyword, not a method.

Jason

4

Jason R. wrote:

On Thu, Nov 6, 2008 at 10:00 AM, Emil S. [email protected] wrote:

yield if condition

Posted via http://www.ruby-forum.com/.

Not possible. ‘while’ is a keyword, not a method.

Jason

Too bad. I thought you could do anything with ruby :wink:

Emil

5

A good idea, but isn’t working in my case. If I mock the condition I
change the behaviour of the method under test too much. But thanks
anyway!

6

On Thu, Nov 6, 2008 at 10:00 AM, Emil S. [email protected] wrote:

Hi, is there an easy way to redefine ‘while’. I have a class that uses a
while loop. In my unit test it always evaluates to false (which is
correct). I only want the loop to run once, and the enter. Just like an
if.

As others already noted, while is a keyword not a method. But
depending on how your code is structured you might be able to mock the
condition in your test:

$ cat foo.rb
class Foo
attr_reader :i

def initialize
@i = 0
end

def condition
@i < 10
end

def method
while condition
@i += 1
end
end
end

$ cat foo_spec.rb
require ‘foo’

describe Foo do
it “should loop once” do
f = Foo.new
f.i.should == 0
f.method
f.i.should == 10
end

it “should loop once” do
f = Foo.new
f.should_receive(:condition).and_return(true, false)
f.i.should == 0
f.method
f.i.should == 1
end
end

$ spec foo_spec.rb
…
Finished in 0.008461 seconds
2 examples, 0 failures

7

On 06.11.2008 16:43, Emil S. wrote:

A good idea, but isn’t working in my case. If I mock the condition I
change the behaviour of the method under test too much. But thanks
anyway!

I find your approach suspicious: you write a class with a method whose
regular behavior involves executing a loop. Then, during tests you want
the loop to not loop, i.e. you change the behavior of your method.
Strictly speaking the test result is then meaningless, because you do
not test the behavior of the method that you want to use regularly.

If there is a complex operation in the loop that you want to test
separately you should probably refactor the code. Then you can have
your one off test.

Cheers

robert

8

Emil S. [email protected] writes:

Jason

Too bad. I thought you could do anything with ruby :wink:

No. You’d need a non-broken lisp to do that.

In Common Lisp:

(shadow 'while)
(defmacro while (condition &body body)
`(progn
(format t “In redefined while~%”)
(when ,condition
,@body)))

(while t
'hi)
In redefined while
HI

9

William J. wrote:

2 3 4 5 6 7 8 redefined REPEAT with repeat
2

redefined REPEAT with repeat 2 3 4 5 6 7 8
2

10

Robert K. wrote:

On 06.11.2008 16:43, Emil S. wrote:

I find your approach suspicious: you write a class with a method whose
regular behavior involves executing a loop. Then, during tests you want
the loop to not loop, i.e. you change the behavior of your method.
Strictly speaking the test result is then meaningless, because you do
not test the behavior of the method that you want to use regularly.

If there is a complex operation in the loop that you want to test
separately you should probably refactor the code. Then you can have
your one off test.

Cheers

robert

That is probably a good idea.

11

On 2008-11-06, Pascal J. Bourguignon [email protected] wrote:

Not possible. ‘while’ is a keyword, not a method.

Jason

Too bad. I thought you could do anything with ruby :wink:

No. You’d need a non-broken lisp to do that.

In Common Lisp:

Now now, Pascal; William J. is a Usenet problem, not a comp.lang.ruby
problem. It doesn’t make sense to retaliate in this way. :slight_smile:

12

Pascal J. Bourguignon wrote:

Not possible. ‘while’ is a keyword, not a method.

Jason

Too bad. I thought you could do anything with ruby :wink:

No. You’d need a non-broken lisp to do that.

No, you wouldn’t. For real extensibility, you need Forth.

In Common Lisp:

A.k.a. Commune Lisp, Committee Lisp, and COBOL Lisp.

In redefined while
HI

GForth:

variable x

: try1 2 x !
begin
x @ 9 <
while
x @ .
1 x +!
repeat ;

: repeat 2drop drop postpone then ; immediate

: try2 2 x !
begin
x @ 9 <
while
x @ .
1 x +!
repeat ;

try1 cr try2

2 3 4 5 6 7 8 redefined REPEAT with repeat
2