puppetlabs/puppet · error · ArgumentError

Expected an Array or String, got a %{klass}

Error message

Expected an Array or String, got a %{klass}

What it means

Puppet::Settings::ArraySetting#munge normalizes values for :type => :array settings: a String is split on /\s*,\s*/ into elements, an Array passes through, and any other class (Integer, Hash, true, Symbol...) raises ArgumentError. Munging happens when the value is converted on read, so the error surfaces at lookup time, not at assignment time.

Source

Thrown at lib/puppet/settings/array_setting.rb:15

# frozen_string_literal: true

class Puppet::Settings::ArraySetting < Puppet::Settings::BaseSetting
  def type
    :array
  end

  def munge(value)
    case value
    when String
      value.split(/\s*,\s*/)
    when Array
      value
    else
      raise ArgumentError, _("Expected an Array or String, got a %{klass}") % { klass: value.class }
    end
  end
end

View on GitHub (pinned to e227c27540)

Solutions

1. Pass a comma-separated String ('a,b,c') or a real Array (['a','b','c']) for array-typed settings.
2. Fix the producer of the value (template/CLI wrapper) so it never emits Integer/boolean/Hash for these keys.
3. If you control the setting, verify its declaration uses :type => :array and all callers honor that.

Example fix

# before
Puppet.settings[:mylist] = 5

# after
Puppet.settings[:mylist] = 'a,b,c'
# or
Puppet.settings[:mylist] = %w[a b c]

unless value.is_a?(String) || value.is_a?(Array)
  raise ArgumentError, "array setting expects String or Array, got #{value.class}"
end
Puppet.settings[:mylist] = value

array_setting_input = ->(v) { v.is_a?(String) || v.is_a?(Array) }

begin
  Puppet.settings[:mylist] = value
rescue ArgumentError => e
  raise unless e.message.include?('Expected an Array or String')
  Puppet.settings[:mylist] = Array(value) # or value.to_s
end

When it happens

Trigger: Setting an array-typed setting to an integer or boolean from code (Puppet.settings[:mylist] = 5); YAML-sourced config producing a Hash where a list was expected; CLI override `--mylist 5` parsed to an Integer before munging.

Common situations: Automated config generation (Hiera-backed templates) writing scalars into list settings; environment differences where one host passes a string 'a,b' and another passes JSON-parsed numbers; refactors changing a value's type.

Related errors

• Invalid value '%{value}' for boolean parameter: %{name}
• Illegal format '#{actual}' specified for value of Array type
• #{subject} #{what},
• key is a %{klass}, not a string or symbol
• Invalid instance type %{klass}, expected %{model_type}

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/1b5e7438cdd561c5. Report an issue: GitHub.