# Ruby wish list item: more standard rescues

**URL:** <https://www.ruby-forum.com/t/ruby-wish-list-item-more-standard-rescues/154222>\
**Category:** Ruby\
**Created:** [November 26, 2008, 3:30pm UTC](https://www.ruby-forum.com/t/ruby-wish-list-item-more-standard-rescues/154222 "2008-11-26T15:30:28Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![rogerdpack](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/45deac/32.png) [@rogerdpack](https://www.ruby-forum.com/u/rogerdpack)\
**Post date:** [November 26, 2008, 3:30pm UTC](https://www.ruby-forum.com/t/ruby-wish-list-item-more-standard-rescues/154222/1 "2008-11-26T15:30:28Z")

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Currently in Ruby

begin  
…  
rescue  
end

which I believe rescues different classes exceptions than

begin  
…  
rescue =\> e  
end

and

begin  
…  
rescue Exception  
end

which always surprises me. Any preferences over always rescuing  
Exception?  
For example, Timeout::Error doesn’t get caught.  
Thanks!  
-=R

---

<div class="post-metadata">

**Author:** ![rogerdpack](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/45deac/32.png) [@rogerdpack](https://www.ruby-forum.com/u/rogerdpack)\
**Post date:** [November 26, 2008, 3:58pm UTC](https://www.ruby-forum.com/t/ruby-wish-list-item-more-standard-rescues/154222/2 "2008-11-26T15:58:00Z")

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Roger P. wrote:

> which always surprises me. Any preferences over always rescuing  
> Exception?

It looks pretty consistent to me. The default is to catch StandardError,  
and most “normal” errors are subclasses of this. Only gross system-level  
errors are outside of this, and you probably didn’t want to catch them  
anyway.

There was talk of ruby-1.9 moving NoMethodError outside of StandardError

- or at least, (x rescue y) not catching it - but a test suggests that  
hasn’t been done.

Anyway, here’s a program you can use to demonstrate how consistent it  
is. If you can show something inconsistent, please update the code to  
show it.

require ‘timeout’

RAISERS = [  
[“timeout error”, lambda { raise Timeout::Error }],  
[“bad method name”, lambda { zxkjcnvkj }],  
[“divide by zero”, lambda { 1/0 }],  
[“Exception”, lambda { raise Exception }],  
]

CATCHERS = [  
[“rescue blank”, lambda { |r|  
begin  
r.call  
rescue  
end  
}],  
[“rescue =\> e”, lambda { |r|  
begin  
r.call  
rescue =\> e  
end  
}],  
[“rescue StandardError”, lambda { |r|  
begin  
r.call  
rescue StandardError  
end  
}],  
[“expr rescue expr”, lambda { |r|  
r.call rescue nil  
}],  
[“rescue Exception”, lambda { |r|  
begin  
r.call  
rescue Exception  
end  
}],  
]

CATCHERS.each do |c|  
puts “\*\*\* For #{c.first}”  
RAISERS.each do |r|  
begin  
c[1].call(r[1])  
rescue Exception  
puts " Didn’t catch #{r[0]}"  
else  
puts " Caught #{r[0]}"  
end  
end  
end

$ ruby raiser.rb  
\*\*\* For rescue blank  
Caught timeout error  
Caught bad method name  
Caught divide by zero  
Didn’t catch Exception  
\*\*\* For rescue =\> e  
Caught timeout error  
Caught bad method name  
Caught divide by zero  
Didn’t catch Exception  
\*\*\* For rescue StandardError  
Caught timeout error  
Caught bad method name  
Caught divide by zero  
Didn’t catch Exception  
\*\*\* For expr rescue expr  
Caught timeout error  
Caught bad method name  
Caught divide by zero  
Didn’t catch Exception  
\*\*\* For rescue Exception  
Caught timeout error  
Caught bad method name  
Caught divide by zero  
Caught Exception

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<div class="post-metadata">

**Author:** ![rogerdpack](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/45deac/32.png) [@rogerdpack](https://www.ruby-forum.com/u/rogerdpack)\
**Post date:** [December 3, 2008, 4:41pm UTC](https://www.ruby-forum.com/t/ruby-wish-list-item-more-standard-rescues/154222/3 "2008-12-03T16:41:41Z")

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Brian C. wrote:

> There was a mistake there, the Timeout::Error line should say
> 
> [“timeout error”, lambda { raise Timeout::Error, “hello” }],
> 
> You’re right that this isn’t a subclass of StandardError and isn’t  
> caught. It’s a subclass of Interrupt. You can argue whether that was a  
> good design decision or not - but since a Timeout::Error means that a  
> thread was aborted mid-way at some arbitrary point, it’s definitely an  
> unusual case.
> 
> There are plenty of posts about why the entire timeout library is broken  
> anyway.

Yeah that one is the the kicker, and it is definitely broken. Any  
thoughts on making it descend from StandardError? [I want to propose it, as some others do…]  
Thanks!  
-=R  
[http://rubyforge.org/tracker/?func=detail&atid=1698&aid=21239&group\_id=426](http://rubyforge.org/tracker/?func=detail&atid=1698&aid=21239&group_id=426)

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<div class="post-metadata">

**Author:** ![rogerdpack](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/45deac/32.png) [@rogerdpack](https://www.ruby-forum.com/u/rogerdpack)\
**Post date:** [November 26, 2008, 4:05pm UTC](https://www.ruby-forum.com/t/ruby-wish-list-item-more-standard-rescues/154222/4 "2008-11-26T16:05:37Z")

</div>

There was a mistake there, the Timeout::Error line should say

[“timeout error”, lambda { raise Timeout::Error, “hello” }],

You’re right that this isn’t a subclass of StandardError and isn’t  
caught. It’s a subclass of Interrupt. You can argue whether that was a  
good design decision or not - but since a Timeout::Error means that a  
thread was aborted mid-way at some arbitrary point, it’s definitely an  
unusual case.

There are plenty of posts about why the entire timeout library is broken  
anyway.