From: Trevor Squires <trevor@...>
Date: 2006-03-13T10:59:03+09:00
Subject: Re: Array#inject with hash as initial, unexpected error

Hey Matthew,

observe:

irb(main):001:0> [] << 100
=> [100]
irb(main):002:0> {}[:something] = 100
=> 100

The << operator on an array returns the array, while the [] operator  
on a hash returns the value you assigned.

And the result of the last statement in your inject block will  
replace the value for your memo on each iteration.

So... just make sure the last statement in your inject block is the  
memo value you are accumulating:

[1,2,3].inject({}) { |memo, val| memo[val] = val**2; memo}

HTH,
Trevor
--
Trevor Squires
http://somethinglearned.com



On 12-Mar-06, at 5:45 PM, Matthew Moss wrote:

> (On Mac OS X 10.4.5, Ruby 1.8.4)
>
>  Okay, so:
>
>> [1, 2, 3].inject(0) { |s, v| s += v }
> => 6
>
> and:
>
>> [1, 2, 3].inject([]) { |a, v| a << v**2 }
> => [1, 4, 9]
>
> but:
>
>> [1, 2, 3].inject({}) { |h, v| h[v] = v**2 }
> => NoMethodError: undefined method `[]=' for 1:Fixnum
>
>
> What gives?
> I've tried replacing {} with Hash.new and a couple other variants  
> without luck.
>