From: Ralph Shnelvar <ralphs@...32.com>
Date: 2012-05-01T05:52:33+09:00
Subject: Question about array of hashes

I'm looking at  Page 39 of Why's (poignant) Guide to Ruby ( http://www.rubyinside.com/media/poignant-guide.pdf ) and I see

[:shape => 'sock', :fabric => 'cashmere'] +
[:shape => 'mouse', :fabric => 'calico'] +
[:shape => 'eggroll', :fabric => 'chenille']

The result of this is (irb 1.9.2)

irb(main):001:0> kitty_toys =
irb(main):002:0* [:shape => 'sock', :fabric => 'cashmere'] +
irb(main):003:0* [:shape => 'mouse', :fabric => 'calico'] +
irb(main):004:0* [:shape => 'eggroll', :fabric => 'chenille']
=> [{:shape=>"sock", :fabric=>"cashmere"}, {:shape=>"mouse", :fabric=>"calico"}, {:shape=>"eggroll", :fabric=>"chenille"}]
irb(main):024:0> kitty_toys.size
=> 3

That is, it is an array of 3 hashes

But the lexically similar

irb(main):001:0> x=
irb(main):002:0* [1, :fabric => 'cashmere'] +
irb(main):003:0* [2, :fabric => 'calico'] +
irb(main):004:0* [3, :fabric => 'chenille']
=> [1, {:fabric=>"cashmere"}, 2, {:fabric=>"calico"}, 3, {:fabric=>"chenille"}]
irb(main):005:0> x.size
=> 6

produces what is to me a surprisingly different result.

Clearly, ruby has flattened things for x and yet ... it seems to have kept the hashes together for kitty_toys

I would have expected

irb(main):006:0> y = [[1, {:fabric=>"cashmere"}], [2, {:fabric=>"calico"}], [3, {:fabric=>"chenille"}]]
=> [[1, {:fabric=>"cashmere"}], [2, {:fabric=>"calico"}], [3, {:fabric=>"chenille"}]]
irb(main):007:0> y.size
=> 3

In fact, the more I stare at it, the more I think that the correct syntax should be

doggy_toys =
[{:shape => 'sock', :fabric => 'cashmere'}] +
[{:shape => 'mouse', :fabric => 'calico'}] +
[{:shape => 'eggroll', :fabric => 'chenille'}]

Why is the kitty_toys syntax even legal?

I see that using the new 1.9 syntax for creating hash tables also works the same way.

irb(main):018:0> birdy_toys =
irb(main):019:0* [shape:'sock', fabric:'cashmere'] +
irb(main):020:0* [shape:'mouse', fabric:'calico'] +
irb(main):021:0* [shape:'eggroll', fabric:'chenille']
=> [{:shape=>"sock", :fabric=>"cashmere"}, {:shape=>"mouse", :fabric=>"calico"}, {:shape=>"eggroll", :fabric=>"chenille"}]
irb(main):022:0> doggy_toys == birdy_toys
=> true

So what are the rules for "implied hash table"?  Where would I find that documented?

Ralph Shnelvar