From: mental@...
Date: 2006-01-26T00:34:51+09:00
Subject: Re: LazyLoad

Quoting Erik Veenstra <google@erikveen.dds.nl>:

> > Will normal code be able to distiguish exceptions raised by
> > implicitly evaluated code at random locations from those
> > which are expected?
>
> I don't get this. Can you please explain a bit more
> specifically, please?

For example (not a great example, but hopefully you'll get a feel
for the issue):

 MAPPING = lazy {
   Hash[*File.read( 'mapping.txt' ).map { |line|
     line.chomp.split
   } ].freeze
 }

 ...

 data = nil
 begin
   File.open( 'data.txt', 'r' ) { |stream|
     data = stream.map { |line| MAPPING[line.chomp] }
   }
 rescue Errno::ENOENT
   # create initial data.txt if it doesn't exist
   File.open( 'data.txt', 'w' ) { |stream|
     MAPPING.keys.each { |key| stream.puts key }
   }
   data = MAPPING.values
 end

Nuking data.txt is probably not the right response to a missing
mapping.txt...

-mental