type-ruby.rb

def int(name)
  eval <<-EOS
    public
    def #{name}=(value)
      raise '#{name} is required' if value == nil
      raise 'Type is mismatch' unless value.is_a? Integer
      @#{name} = value
    end
  EOS
end

def string(name)
  eval <<-EOS
    public
    def #{name}=(value)
      raise '#{name} is required' if value == nil
      raise 'Type is mismatch' unless value.is_a? String
      @#{name} = value
    end
  EOS
end

def string?(name)
  eval <<-EOS
    public
    def #{name}=(value)
      raise 'Type is mismatch' unless value == nil || value.is_a?(String)
      @#{name} = value
    end
  EOS
end

class Example
  int :id
  string :name
  string? :description
end

Example.new.id = 3
Example.new.id = "3"
Example.new.id = nil
Example.new.description = 3
Example.new.description = "3"
Example.new.description = nil