Initialize returning nil if error condition - how

[Graham Nicholls]

I've got "The Ruby Way" & "Programming Ruby", but can't find out how to have
an initializer return nil if theres a problem - something like this:

Class Cover_file
def initialize(fname)
64 @fname=fname
65 if $verbose
66 printf("Checking file %s\n",@fname)
67 end
68 # Parse filename for component parts
(product,policy_no,site_no,schedule)
69 comp_patt=Regexp.compile(/^([A-Z]+)([0-9]+)([0-9][0-9]
([\w\d]+)\.en$/)
70 if @fname !~ comp_patt
71 if $verbose
72 printf("Sorry, %s does not match cover clause filename
template\n",fname)
73 end
74 return nil

If I try self=nil, I (not unreasonably - I expected it) get an error.

What I want to do is this:

cfile=Cover_file.new(fname)
if cfile == nil
some error handling
end

But I can't work out how.
Thanks.
Graham Nicholls

 

[Graham Nicholls]

I've got "The Ruby Way" & "Programming Ruby", but can't find out how to
have an initializer return nil if theres a problem - something like this:

Class Cover_file
def initialize(fname)
64 @fname=fname
65 if $verbose
66 printf("Checking file %s\n",@fname)
67 end
68 # Parse filename for component parts
(product,policy_no,site_no,schedule)
69 comp_patt=Regexp.compile(/^([A-Z]+)([0-9]+)([0-9][0-9]
([\w\d]+)\.en$/)
70 if @fname !~ comp_patt
71 if $verbose
72 printf("Sorry, %s does not match cover clause filename
template\n",fname)
73 end
74 return nil

If I try self=nil, I (not unreasonably - I expected it) get an error.

What I want to do is this:

cfile=Cover_file.new(fname)
if cfile == nil
some error handling
end

But I can't work out how.
Thanks.
Graham Nicholls

Just had an idea (thats the 2nd time I've done that this week! (not had an
idea, fools, commented on my own post!). I'm supposed to raise an error,
aren't I?
Thanks
Graham

 

[Robert Klemme]

I've got "The Ruby Way" & "Programming Ruby", but can't find out how to
have an initializer return nil if theres a problem - something like this:

Class Cover_file
def initialize(fname)
64 @fname=fname
65 if $verbose
66 printf("Checking file %s\n",@fname)
67 end
68 # Parse filename for component parts
(product,policy_no,site_no,schedule)
69 comp_patt=Regexp.compile(/^([A-Z]+)([0-9]+)([0-9][0-9]
([\w\d]+)\.en$/)
70 if @fname !~ comp_patt
71 if $verbose
72 printf("Sorry, %s does not match cover clause filename
template\n",fname)
73 end
74 return nil

If I try self=nil, I (not unreasonably - I expected it) get an error.

What I want to do is this:

cfile=Cover_file.new(fname)
if cfile == nil
some error handling
end

But I can't work out how.
Thanks.
Graham Nicholls

Just had an idea (thats the 2nd time I've done that this week! (not had an
idea, fools, commented on my own post!). I'm supposed to raise an error,
aren't I?

Yes, that's the proper way to deal it. Exceptions make code much cleaner
if properly used.

Regards

robert

 

[nobu.nokada]

Hi,

At Tue, 6 Jul 2004 16:37:49 +0900,
Graham Nicholls wrote in [ruby-talk:105342]:

I've got "The Ruby Way" & "Programming Ruby", but can't find out how to have
an initializer return nil if theres a problem - something like this:

Default Class#new always returns created instance unless any
exceptions occurred. What you want isn't impossible by your
own "new" class method, but raising an exception in
"initialize" is much better.

class CoverFile
def initialize(fname)
end
def self.new(*args, &block)
if obj = allocate()
obj.__send__(*args, &block)
end
obj
end
end