How do I enforce variable declarations in Ruby?

ruby-talk
1

Is there any way to require that all variables and class attributes be
predeclared? I’m looking for something similar to Perl’s strict
pragma. It would prevent bugs like this:

class Demo
def initialize
@count = 0
end

def anotherfunc
    @cout += 1
end

def get_count
    @count
end

end

d = Demo.new
puts d.get_count
d.anotherfunc
d.get_count

Note the typo in anotherfunc. This code was intended to output a zero
followed by a one, but because of the typo, will output two 0’s.

Is there any way to prevent errors like this from happening? I find
it hard to believe that a language as well-designed as Ruby would lack
this simple feature.

2

“Bill Atkins” dejaspam@batkins.com schrieb im Newsbeitrag
news:e6056acc.0403090356.7654b195@posting.google.com…

Is there any way to require that all variables and class attributes be
predeclared? I’m looking for something similar to Perl’s strict
pragma. It would prevent bugs like this:

class Demo
def initialize
@count = 0
end

def anotherfunc
    @cout += 1
end

def get_count
    @count
end

end

d = Demo.new
puts d.get_count
d.anotherfunc
d.get_count

Note the typo in anotherfunc. This code was intended to output a zero
followed by a one, but because of the typo, will output two 0’s.

Well, you get at least this:

irb(main):017:0> d.anotherfunc
NoMethodError: undefined method +' for nil:NilClass from (irb):7:in anotherfunc’
from (irb):17
irb(main):018:0> d.get_count
=> 0
irb(main):019:0>

Isn’t that verbose enough?

Is there any way to prevent errors like this from happening? I find
it hard to believe that a language as well-designed as Ruby would lack
this simple feature.

Alternatively you can do this:

class Demo
attr_accessor :count
private :count=

def initialize
    self.count = 0
end

def anotherfunc
    self.cout += 1
end

end

Which some would regard cleaner OO anyway. This yields

irb(main):034:0> d.anotherfunc
NoMethodError: undefined method cout' for #<Demo:0x1018f550 @count=0> from (irb):27:in anotherfunc’
from (irb):34

Btw: If you have a well designed unit test, either error will show up
during testing.

Regards

robert
···

from :0

3

Is there any way to require that all variables and class attributes be
predeclared? I’m looking for something similar to Perl’s strict
pragma. It would prevent bugs like this:

class Demo
def initialize
@count = 0
end

def anotherfunc
    @cout += 1
end

def get_count
    @count
end

end

d = Demo.new
puts d.get_count
d.anotherfunc
d.get_count

Note the typo in anotherfunc. This code was intended to output a zero
followed by a one, but because of the typo, will output two 0’s.

Is there any way to prevent errors like this from happening?

method one - use ruby’s ability to declare accessors

~ > cat a.rb
class Demo
attr :count, 1
def initialize
self.count = 0
end
def anotherfunc
self.cout += 1
end
def get_count
self.count
end
end

d = Demo.new
puts d.get_count
d.anotherfunc
d.get_count

~ > ruby a.rb
0
a.rb:7:in anotherfunc': undefined method cout’ for #<Demo:0x400a3cc8 @count=0> (NoMethodError)
from a.rb:16

method two - turn on warnings

~ > cat b.rb
$VERBOSE = true
class Demo
def initialize
@count = 0
end
def anotherfunc
@cout += 1
end
def get_count
@count
end
end

d = Demo.new
puts d.get_count
d.anotherfunc
d.get_count

~ > ruby b.rb
0
b.rb:8: warning: instance variable @cout not initialized
b.rb:8:in anotherfunc': undefined method +’ for nil:NilClass (NoMethodError)
from b.rb:17

I find it hard to believe that a language as well-designed as Ruby would
lack this simple feature.

it’s the ‘-w’ switch ($VERBOSE = true)

-a

···

On 9 Mar 2004, Bill Atkins wrote:

===============================================================================

EMAIL :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
PHONE :: 303.497.6469
ADDRESS :: E/GC2 325 Broadway, Boulder, CO 80305-3328
URL :: Solar-Terrestrial Physics Data | NCEI
TRY :: for l in ruby perl;do $l -e “print "\x3a\x2d\x29\x0a"”;done
===============================================================================

4

Bill Atkins wrote:

Is there any way to require that all variables and class attributes be
predeclared?

Is there any way to prevent errors like this from happening?

require ‘test/unit’

and code test first. After four(?) years of using Ruby, I have yet to
find out how to use it’s debugger.

Regards,

···

–
Bil Kleb, NASA, Hampton, Virginia