From: Eric Hodel <drbrain@...7.net>
Date: 2006-03-08T07:47:05+09:00
Subject: Re: Rescue on do end blocks

On Mar 7, 2006, at 4:31 AM, Farrel Lifson wrote:

> I've been playing around with rescue expressions and besides being put
> on functions they also seem to work when defining classes (useful for
> metaprogramming perhaps?)

[...]

> However, why can they not be applied to do end blocks?
>
> irb(main):016:0> [1,2,3].each do |num|
> irb(main):017:1*   num.upcase
> irb(main):018:1> rescue
> irb(main):019:1>   puts "Error"
> irb(main):020:1> ensure
> irb(main):021:1*   puts "Clened up"
> irb(main):022:1> end
> SyntaxError: compile error
> (irb):18: syntax error
> (irb):20: syntax error
>         from (irb):22

This will make blocks much more expensive to call because you'll have  
to perform the exception handler setup and teardown for each  
invocation of the block which will give a slight performance  
degradation:

require 'benchmark'

N = 10_000_000

Benchmark.bmbm do |bm|
   bm.report 'without begin' do N.times { 0 } end
   bm.report 'with begin' do N.times { begin 0 end } end
   bm.report 'with rescue' do N.times { begin 0; rescue; end } end
end

                     user     system      total        real
without begin   4.520000   0.020000   4.540000 (  4.939785)
with begin      5.000000   0.030000   5.030000 (  6.050101)
with rescue     6.720000   0.030000   6.750000 (  7.716410)

While having an implicit begin won't give the same level of slowdown  
if implemented in the compiler, there's no pressing need to add the  
complexity to Ruby because it isn't the common case.

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant

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