steep example

temperature.rb

class Temperature
  # @implements Temperature

  private_class_method :new

  def self.celsius(num)
    new(num)
  end

  def self.fahrenheit(num)
    new(f2c(num))
  end

  def self.f2c(f)
    (f - 32) / 1.8
  end

  def self.c2f(c)
    c * 1.8 + 32
  end

  # @type ivar @celsius: Numeric
  def initialize(num)
    @celsius = num
  end

  def celsius
    @celsius
  end

  def celsius_label
    "摂氏#{@celsius}度"
  end

  def fahrenheit
    self.class.c2f(celsius)
  end

  def fahrenheit_label
    "華氏#{fahrenheit}度"
  end
end

temperature.rbi

class Temperature
  def (constructor) self.celsius: (Numeric) -> instance
  def (constructor) self.fahrenheit: (Numeric) -> instance

  def self.f2c: (any) -> Numeric
  def self.c2f: (any) -> Numeric

  def initialize: (Numeric) -> any

  def celsius: -> Numeric
  def celsius_label: -> String
  def fahrenheit: -> Numeric
  def fahrenheit_label: -> String
end

extension Class (X)
  def private_class_method: (Symbol) -> any
end

test_temperature.rb

require 'minitest/autorun'
require './temperature'

class TestTemperature < Minitest::Test
  def test_celsius
    subject = Temperature.celsius(34)
    assert_equal subject.celsius, 34
  end

  def test_zero
    zero = Temperature.celsius(0)
    assert_equal zero.fahrenheit, 32
  end

  def test_zero2
    zero = Temperature.fahrenheit(32)
    assert_equal zero.celsius, 0
  end

  def test_handred
    handred = Temperature.celsius(100)
    assert_equal handred.fahrenheit, 212
  end

  def test_handred2
    handred = Temperature.fahrenheit(212)
    assert_equal handred.celsius, 100
  end

  def test_fahrenheit
    subject = Temperature.fahrenheit(12)
    assert_equal subject.fahrenheit, 12
  end

  def test_celsius_label
    zero = Temperature.celsius(0)
    assert_equal zero.celsius_label, "摂氏0度"
  end

  def test_celsius_label
    zero = Temperature.celsius(0)
    assert_equal zero.fahrenheit_label, "華氏32.0度"
  end
end

steep checkを実行してみると NoMethodError が出てしまう

% steep check -I temperature.rbi temperature.rb
temperature.rb:7:4: NoMethodError: type=Temperature.module, method=new
temperature.rb:11:4: NoMethodError: type=Temperature.module, method=new