class Fixnum
    def to_f
        # …
    end
end

vede k

class String
    def to_s
    def to_str
    def to_sym
    def to_i
    def to_d
    def to_f
    def to_a
    def to_enum
    def to_set
    def to_param
    def to_query
    def to_json
    def to_xs
    def to_yaml
    def to_yaml_proprties
    def to_yaml_style
    def to_blob
    def to_date
    def to_time
    # …
end

class File
    def initialize(file_path)
        # …
    end
end

File.new "/tmp"

class Date
    def self.from_string(a_string)
        # …
        Date.new # with the righ args
    end
end
Date.from_string "2009-03-14"
Date.from_julian_string "-4712-03-01"

Converter Constructor Method