From: Logan Capaldo <logancapaldo@...>
Date: 2006-06-07T14:43:45+09:00
Subject: Re: What's going on here? (Newbie question)


On Jun 6, 2006, at 9:42 PM, Mike Stok wrote:

>
> On 6-Jun-06, at 9:36 PM, MB wrote:
>
>> In irb:
>>
>> f = File.new('numbers.txt')
>> => #<File:numbers.txt>
>>
>> f.each {|line| puts line}
>> 123
>> 456
>> 789
>> => #<File:numbers.txt>
>>
>> f.each {|line| puts line}
>> => #<File:numbers.txt>
>>
>> Why doesn't the second f.each work?
>
> because as each iterates through the file it "consumes" the file  
> contents (well, it remembers how far it has got.)  You can usually  
> rewind a file to the beginning, so:
>
> irb(main):001:0> f = File.new('numbers.txt')
> => #<File:numbers.txt>
> irb(main):002:0> f.each {|line| puts line}
> 123
> 456
> 789
> => #<File:numbers.txt>
> irb(main):003:0> f.pos
> => 12
> irb(main):004:0>  f.each {|line| puts line}
> => #<File:numbers.txt>
> irb(main):005:0> f.pos
> => 12
> irb(main):006:0> f.rewind
> => 0
> irb(main):007:0>  f.each {|line| puts line}
> 123
> 456
> 789
> => #<File:numbers.txt>
>
> Note that some types of file can't be rewound.
>
> Take a look at what the pos method does, and see if this makes sense.
>
> Hope this helps,
>
> Mike
>
> -- 
>
> Mike Stok <mike@stok.ca>
> http://www.stok.ca/~mike/
>
> The "`Stok' disclaimers" apply.
>
>
>
>
>

I wonder if IO#each should be changed to automatically #rewind at the  
beginning of #each (if possible). I have difficulty imagining a  
situation where someone would purposely do
a = file.gets
file.each { ... }

But I can certainly imagine people iterating over a file multiple  
times. OTOH this may be too magical.