From: Bryan Weatherly <bryan.weatherly.ruby@...>
Date: 2006-06-07T22:10:50+09:00
Subject: Re: What's going on here? (Newbie question)


On Jun 6, 2006, at 11:43 PM, Logan Capaldo wrote:

>
> 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.
>
>

What about using:

f = IO.readlines(file)

Then the entire file contents will be loaded line-by-line as an  
array.  You wouldn't have to worry about rewinding the position in  
the actual file.