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This gem helps to define callable classes with strict params specification.


Add this line to your application's Gemfile:

gem 'callee'

And then execute:

$ bundle

Or install it yourself as:

$ gem install callee


To make a class callable, you need to include Callee mixin and implement call instance method. Use dry-initializer DSL to specify calling parameters and options if necessary. Here is a basic usage example:

class Power
  include Callee

  # Required parameter
  param :base

  # Option with a default value
  option :exponent, optional: true, default: -> { 2 }

  def call
end  # => 4, exponent: 10)  # => 1024

Callable class may be used as a Proc. Compact notation in the next example is identical to [1, 2, 3].map { |value| }

[1, 2, 3].map(&Power)  # => [1, 4, 9]

Since Callee mixin inherits dry-initializer DSL, type constraints and coercion will also work, as usual. Just make sure to include dry-types:

require "dry-types"

class StrictPower
  include Callee

  param :base, type: Dry::Types["strict.integer"]
  option :exponent, type: Dry::Types["strict.integer"], optional: true, default: -> { 2 }

  def call

# Let's inherit StrictPower params definition
# and override "base" with more forgiving constraint
class CoerciblePower < StrictPower
  param :value, type: Dry::Types["coercible.integer"]

string_values = %w[1 2 3]  # Will raise Dry::Types::ConstraintError  # => [1, 4, 9]

See more examples in dry-rb docs.


After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.