From: Logan Capaldo <logancapaldo@...>
Date: 2006-02-01T12:50:33+09:00
Subject: Re: memoize to a file


On Jan 31, 2006, at 10:32 PM, Brian Buckley wrote:

> Hello all,
>
> Using Memoize gem 1.2.0, memoizing TO a file appears to be working  
> for me
> but subsequently reading that file (say, by rerunning the same script)
> appears NOT to be working  (the fib(n) calls are being run again).
> Inspecting the Memoize module I changed the line
>
> cache = Hash.new.update(Marshal.load(File.read(file))) rescue { }
> to
> cache = Hash.new.update(Marshal.load(File.read(file)))
>
> and it instead of silently failing I now see the error message: "in  
> `load':
> marshal data too short (ArgumentError)"
>
> My questions:
> 1  What is causing this error? (possibly Windows related?)
> 2  What is the purpose of the rescue{} suppressing the error info  
> in the
> first place?
> 3  Instead of using Marshall would using yaml be a reasonable  
> alternative?
> (I am thinking of readability of the cache file and also capability to
> pre-populate it)
>
> Thanks.
>
> -- Brian Buckley
>
> ------------------------------------------
> require 'memoize'
> include Memoize
> def fib(n)
>   puts "running... n is #{n}"
>   return n if n < 2
>   fib(n-1) + fib(n-2)
> end
> h = memoize(:fib,"fib.cache")
> puts fib(10)

Basically it's using exceptions as flow control:

begin
    cache = Hash.new.update(Marshal.load(File.read(file)))
rescue
     cache = {} # empty hash
end

So for whatever reason, if loading the file fails (eg, this is the  
first time the program has been run) it just starts with an empty  
cache. I don't know why its failing to read the file.