Lap

Don't write your code, and rbs types! Write the rbs types first, then generate a template to fill in with business logic.

A lapidary (or lapidist) is someone who cuts, polishes, or engraves precious stones.

Usage

$ lap sig/file.rbs # outputs to stdout
$ lap sig/file.rbs > lib/file.rb # output into a file

Example

1. Plan your project/module/class by writing some blueprints:

   # sig/lib/bank/account.rbs
   module Bank
   class Account
   attr_reader interest_rate: Float
   attr_reader owner: Bank::Customer
   attr_reader balance: Float
   
   type date_or_dt = Date | DateTime
   
   # can optionally specify when the transaction should take place
   def deposit: (Float amount, ?when: date_or_dt) -> Float
   
   # can optionally specify when the transaction should take place
   def withdraw: (Float amount, ?when: date_or_dt) -> Float
   
   # must filter results by specifying `to` and `from` params
   def transactions: (from: date_or_dt, to: date_or_dt) -> Array[Bank::Transaction]
   end
   end
   

2. Generate your ruby templates

$ lap sig/lib/bank/account.rbs > lib/bank/account.rb

(Generates lib/bank/account.rb)

module Bank
  class Account
    attr_reader :interest_rate
    attr_reader :owner
    attr_reader :balance

    def initialize(owner, interest_rate, balance)
        @owner = owner
        @interest_rate = interest_rate
        @balance = balance
    end

    # can optionally specify when the transaction should take place
    def deposit(amount, when: nil)
      # TODO: return Float
    end

    # can optionally specify when the transaction should take place
    def withdraw(amount, when: nil)
      # TODO: return Float
    end

    # must filter results by specifying `to` and `from` params
    def transactions(to:, from:)
      # TODO: return Array
    end
  end
end

1. Fill in your business logic!

module Bank
  class Account
    attr_reader :interest_rate
    attr_reader :owner
    attr_reader :balance

    def initialize(owner, interest_rate, balance)
        @owner = owner
        @interest_rate = interest_rate
        @balance = balance
    end

    # can optionally specify when the transaction should take place
    def deposit(amount, when: nil)
      @balance += amount
    end

    # can optionally specify when the transaction should take place
    def withdraw(amount, when: nil)
      @balance -= amount
    end

    # must filter results by specifying `to` and `from` params
    def transactions(to:, from:)
      Transaction.where("created_at BETWEEN ? AND ?", from, to)
    end
  end
end

From here, you now have some ruby code which you can type check!

Installation

Add this line to your application's Gemfile:

gem 'cutter'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install cutter

Configuration

You can specify preferences in a .lap.yml file in your project directory. Example

indent: 4 # default is 2
# this is it for now, more to come

Coverage

Currently not every feature of RBS is supported - yet! (contributions welcome!)

Feature	Coverage
classes (includes nested)	✅
modules (includes nested)	✅
class methods	✅
instance methods	✅
required positional arguments	✅
optional positional arguments	✅
required keyword arguments	✅
optional keyword arguments	✅
method comments	✅
access modifiers	✅
attr_reader	✅
attr_writer	✅
attr_accessor	✅
include	✅
extend	✅
methods with blocks	✅
method overloading	⚠️
procs	⚠️
constants	⚠️
interfaces	⚠️

Experimental:

There is an experimental feature which allows you to specify some ruby logic within your rbs files for your methods. You specify it between @!begin and @!end, eg.:

# take some moeny out of the customers account
# @!begin
#   @balance -= amount
# @!end
def withdraw(Float amount) -> Float

This would produce:

# take some moeny out of the customers account
def withdraw(amount)
  @balance -= amount
end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec 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 rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/johansenja/lap.

License

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