From: Josh Cheek <josh.cheek@...>
Date: 2010-04-01T04:54:25+09:00
Subject: Re: Weird hash key: what am I asking Ruby to do?

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On Wed, Mar 31, 2010 at 12:32 PM, Aldric Giacomoni <aldric@trevoke.net>wrote:

> I decided to type the following in irb:
> irb(main):010:0> a = {}
> => {}
> irb(main):015:0> a[lambda { x } => 5] = 5
> => 5
> irb(main):016:0> a
> => {{#<Proc:0x028cb304@(irb):15>=>5}=>5}
>
> irb(main):017:0> a = {}
> => {}
> irb(main):018:0> a[lambda { x } ] = 5
> => 5
> irb(main):019:0> a
> => {#<Proc:0x028c2a4c@(irb):18>=>5}
>
> So.. In the first example, the hash key is 'lambda { x } => 5' .
> What on earth does that even mean?
>
>
It means that the key is a hash table which contains a key of the lambda,
that maps to the value of 5. Notice all three sets of code are the same, the
keys just get progressively more complicated looking. But if you didn't know
what they were, and just considered them to be an object (which they are),
then they are no longer so complicated, just complicated looking.

key = 'simple'
hash = Hash.new
hash[ key ] = 5
hash        # => {"simple"=>5}
key[ key ]  # => "simple"

##########

key = lambda {x}
hash = Hash.new
hash[ key ] = 5
hash        # => {#<Proc:0x000332e8@-:9>=>5}
hash[ key ] # => 5

key = hash # the hash from the previous code block is now the key
hash = Hash.new
hash[ key ] = 5
hash        # => {{#<Proc:0x000332e8@-:9>=>5}=>5}
hash[ key ] # => 5

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