Question

nodes = {
  :node1 => { 
    :inherits => nil, 
    :variables => { :foo => 1, :bar => 2 } 
  },
  :node2 => { 
    :inherits => :node1, 
    :variables => { :foo => 9, :baz => 4 } 
  }
}

I’ve been trying to understand how to return a new nodes hash where each node’s :variables hash is merged with :variables from the node specified in :inheritance. In other words, node1 would be left as is while node2 to end up with :variabes => { :foo => 9, :bar => 2, :baz => 4 }

I’ve been swimming through docs involving Enumerable#inject, Hash#merge with a block, and more and figure it’s time to ask for help.

UPDATE:

Figured I’d provide an update. This code is certainly not the solution but it might be heading in the right direction…

nodes = {
  :node1 => { :inherits => nil, :variables => { :foo => 1, :bar => 2 } },
  :node2 => { :inherits => :node1, :variables => { :foo => 9, :baz => 4 } }
}

new = nodes.inject({}) do |result, (k, v)|
  result.merge k => v.merge({ :variables => { :a => 6, :b => 7 } })
end

returns

{:node2=>{:inherits=>:node1, :variables=>{:a=>6, :b=>7}}, :node1=>{:inherits=>nil, :variables=>{:a=>6, :b=>7}}}

So that v.merge is not working as intended…

Answer 1

merged_nodes = {}

nodes.each do |name, node|
  merged_nodes[name] = node.dup
  merged_nodes[name][:variables] = if node[:inherits]
    nodes[node[:inherits]][:variables].merge node[:variables]
  else
    node[:variables].dup
  end
end

will give you

{
  :node1=>{:inherits=>nil, :variables=>{:foo=>1, :bar=>2}},
  :node2=>{:inherits=>:node1, :variables=>{:foo=>9, :bar=>2, :baz=>4}}
}

but it won’t handle deeper nesting i.e. if :node3 then inherits :node2… if you need anything as complicated as that, this hash-based approach is going to get pretty clunky.