Is there a solution to bypass 'can't add a new key into hash during iteration (RuntimeError)'?

I have a big problem with the expected RuntimeError: "can't add a new key into hash during iteration"

In my case a I have a YAML file: test.yaml - in which I have some keys already added.

test.yaml
key1:
key2:
key3:

I am getting the contents of the file in a variable:

file_hash = YAML.load_file("testm.yaml")

Then I need to loop through this hash and add other keys to them:

file_hash.each do |key|
file_hash[key] = 'key_1'
file_hash[key] = 'key_2'
end
File.open('test.yaml', 'w') { |f| YAML.dump(file_hash, f) }

The main issue is that I am unable to write into a hash while in a loop. I don't understand why this is expected, when you have the power to control the loop block.
Is there another way in which I can accomplish what I showed above?

Note: I am using RUBY 1.9.3 p547

I had the same error at

<%= stylesheet_link_tag 'application', 'data-turbolinks-track' => 'reload', media: 'all' %>

So I rewrite my code with:

<% begin %>
<%= stylesheet_link_tag 'application', 'data-turbolinks-track' => 'reload', media: 'all' %>
<%= javascript_include_tag 'application', 'data-turbolinks-track' => 'reload' %>
<% rescue %>
<script>
window.location.replace "#{user_session_url()}"
</script>
<% end %>

I do not know what is causing this issue, but this workaround works for me. I tested it with

ab -n 100 -c 10 -w

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And I did not got any error messages

previous answer didn't help me, so i propouse that help for me

a={1=>1}; a = a.clone; a[2] = 2; a

Ruby since 1.9 is using *lazy* iteration, thus they forbid to add new keys to the *hash* you iterating over. As a solution you can easily duplicate *hash* or convert it to *array* before doing `each`.

irb(main):001:0> a={1=>1}; a.each {|k,v| a[2] = 2}
RuntimeError: can't add a new key into hash during iteration

irb(main):002:0> a={1=>1}; a.clone.each {|k,v| a[2] = 2}; a
=> {1=>1, 2=>2}

irb(main):003:0> a={1=>1}; a.to_a.each {|k,v| a[2] = 2}; a
=> {1=>1, 2=>2}

You're modifying the hash you're iterating over. You can't do it.

Instead try another approach:

keys = [1,2,3,4]
file_hash = YAML.load_file("testm.yaml")
keys.each{ |key| file_hash[key] = 'key1' }
# => {1 => 'key1', 2 => 'key1', 3 => 'key1', 4 => 'key1'}