From: Tim Hunter <TimHunter@...>
Date: 2009-06-06T10:40:10+09:00
Subject: Re: Can someone explain the difference: Array[] and Array.fetch

Marc Heiler wrote:
> array = ["a","b","c"]        # => ["a", "b", "c"]
> array[1]                     # => "b"
> array.fetch 1                # => "b"
> 
> 
> # ================================================== #
> # So far, so fine.
> # ================================================== #
> 
> 
> array[666]                   # => nil
> array.fetch 666
> 
> IndexError: index 666 out of array
>         from (irb):5:in `fetch'
>         from (irb):5
> 
> 
> This may seem like a trival difference between the two, but
> I am wondering in general why they behave differently.
> Or in other words, why array[] does not return an error
> whereas .fetch specifically does.

You might say that's the purpose of fetch, to raise an exception for 
out-of-bounds indexes when [] just returns nil. Pick the method you want 
depending on the error handling you want.

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