# Ruby style question from a newby: exceptions

**URL:** <https://www.ruby-forum.com/t/ruby-style-question-from-a-newby-exceptions/48149>\
**Category:** Ruby\
**Created:** [November 17, 2005, 4:27am UTC](https://www.ruby-forum.com/t/ruby-style-question-from-a-newby-exceptions/48149 "2005-11-17T04:27:34Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![richard.j.cole](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/7ba0ec/32.png) [@richard.j.cole](https://www.ruby-forum.com/u/richard.j.cole)\
**Post date:** [November 17, 2005, 4:27am UTC](https://www.ruby-forum.com/t/ruby-style-question-from-a-newby-exceptions/48149/1 "2005-11-17T04:27:34Z")

</div>

Hi,

Any hints on the best way to catch exceptions from the point of view of  
good style for the following?

* * *

puts “Create connection…”  
imap = IMAP.new(‘[sslmail.somewhere.com](http://sslmail.somewhere.com)’, 993, true)  
puts “Capabilities: cap = #{imap.capability().join(” “)}”  
puts “Authenticate…”  
logged\_in = false

begin  
imap.authenticate(‘CRAM-MD5’, ‘myname’, ‘secret’)  
logged\_in = true  
rescue Net::IMAP::NoResponseError =\> e  
puts " Failed, #{e}"  
end

## puts “Try Login…” if ! logged\_in then begin imap.login(‘myname’, ‘secret’) logged\_in = true rescue puts " Failed, #{e}" end end

What am I trying to do and what don’t I like? Basically I want to try a  
sequence of things until one of them works — first I want to use the  
authenticate method and if that fails to use the login method. Each of  
these methods indicates failure by raising an exception. I want to log  
each failure (because I’m experimenting with the library at this  
stage). In this example I want to log each failure and on failure I  
want to cacade to an alternative strategy.

How could this code be better written so that it is easier to read and  
understand the flow of the code? Would it be possible to achieve  
something like the following?

* * *

exceptions = until\_success   
{ imap.authenticate … },  
{ imap.login … }

## if exceptions.failed then puts “Unable to login: #{exceptions.join(‘\n’)}” else puts “Login successfull. Record of unsuccessfull attempts: \n #{exceptions.join(”\n “)}” end

with a function until\_success taking a sequence of blocks as arguments?

regards,

Richard.

---

<div class="post-metadata">

**Author:** ![richard.j.cole](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/7ba0ec/32.png) [@richard.j.cole](https://www.ruby-forum.com/u/richard.j.cole)\
**Post date:** [November 17, 2005, 11:53am UTC](https://www.ruby-forum.com/t/ruby-style-question-from-a-newby-exceptions/48149/2 "2005-11-17T11:53:57Z")

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Is the following irb session informative?

```
irb(main):013:0> c = 0
irb(main):014:0> begin
irb(main):015:1* p c
irb(main):016:1> raise
irb(main):017:1> rescue
irb(main):018:1> c += 1
irb(main):019:1> retry if c < 5
irb(main):020:1> end
1
2
3
4
=> nil
```

---

<div class="post-metadata">

**Author:** ![richard.j.cole](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/7ba0ec/32.png) [@richard.j.cole](https://www.ruby-forum.com/u/richard.j.cole)\
**Post date:** [November 17, 2005, 5:33pm UTC](https://www.ruby-forum.com/t/ruby-style-question-from-a-newby-exceptions/48149/3 "2005-11-17T17:33:13Z")

</div>

YANAGAWA Kazuhisa wrote:

> ```
> irb(main):019:1> retry if c < 5
> 
> ```

Hi Richard,

Here’s a variation on that theme:

#--------------------------------------------------------

METHOD\_Q = [[:aaa, TypeError],  
[:bbb, NoMethodError],  
[:ccc, ArgumentError],  
[:ddd, NameError],  
].freeze

def log(item); puts “LOG: #{item}”; end

def aaa; 11 + ‘Two Two’; end  
def bbb; 12.sort; end  
def ccc; [].each(13) {}; end  
def ddd  
puts “4th attempt”

# NOCONST # \<— uncomment

end

catch(:done) do  
stack = METHOD\_Q.dup  
begin  
meth, exc = stack.shift  
unless meth  
log “Tried everything :(”  
throw(:done)  
end  
send(meth)  
log “Success at last!”  
rescue exc =\> e  
log “#{meth} error”  
log “^ #{e.message}”  
retry  
end  
end

=begin

LOG: aaa error  
LOG: ^ String can’t be coerced into Fixnum  
LOG: bbb error  
LOG: ^ undefined method `sort’ for 12:Fixnum  
LOG: ccc error  
LOG: ^ wrong number of arguments (1 for 0)  
4th attempt  
LOG: Success at last!

=end  
#--------------------------------------------------------

daz