Function to compare hashes

[XMol]

Puppet is incapable of comparing two hashes with each other and I'm very surprised that there is no function in the stdlib tool set to address that either. A function like this seems quite simple to me:

Puppet::Functions.create_function(:cmp_hash) do
  dispatch :cmp_hashes_as_arrays do
    param 'Hash[Any, Any]', :hash
    param 'Hash[Any, Any]', :hash
  end

  dispatch :cmp_hashes_with_block do
    param 'Hash[Any, Any]', :hash
    param 'Hash[Any, Any]', :hash
    block_param 'Callable[1,1]', :block
  end

  def cmp_hashes_as_arrays (h1, h2)
    cmp_hashes_with_block(h1, h2) { |h| h.to_a.sort }
  end

  def cmp_hashes_with_block (h1, h2)
    yield(h1) <=> yield(h2)
  end
end

Given a lambda that transforms a Hash into something that Ruby can compare with <=>, arbitrary Hashes can be compared to each other. If no lambda is given, the functions falls back to casting both Hashes to sorted Arrays and then compare them (which Ruby can do already).

Examples

$hash1 = {
  'primary_key' => 2,
  'key1' => ['val1', 'val2'], 
  'key2' => { 'key3' =>  'val3', }, 
  'key4' => true,
  'key5' => 12345,
 }

$hash2 = {
  'primary_key' => 1,
  'key6' => ['val1', 'val2'], 
  'key7' => { 'key8' =>  'val9', }, 
  'key10' => true,
  'key11' => 67890,
 }

cmp_hash($hash1, $hash2) # => -1; 'key1' is the smallest key, thus $hash1 is smaller
cmp_hash($hash1, $hash2) |$h| { $h['primary_key'] } # => 1; $hash2 has the smaller value for 'primary_key', hence $hash1 is bigger

Now it is also possible to order an Array of Hashes with the built-in sort() function:

$::disks.values.sort |$a, $b| { cmp_hash($a, $b) |$h| { $h['size_bytes'] } }

[binford2k]

I'm surprised you didn't contribute your functions to stdlib.

[XMol]

Because this seems such an obvious omission, I figured that there is a good reason for it that I'm not aware of. Or there simply is no demand for comparing Hashes in Puppet.

[b4ldr]

i dont think there is an equivalent in stdlib or puppet core so +1 for sending a PR

[XMol]

Thanks for the encouragement. 😊 Maybe I'll find the time for making a PR next week.

[XMol]

It took me longer than a week, but a PR is now submitted.

[XMol]

Credits to @smortex, who proposed a solution that a accomplishes the comparison of two Hashes without adding a new function to Puppet:

compare($hash1.dig('primary_key'), $hash2.dig('primary_key'))