class Dia < Date
def initialize(ano, mes, dia, obj_mes) @mes = obj_mes
super(ano, mes, dia)
end
end
a = Dia.new
=> #<Dia: -4712-01-01 ((0j,0s,0n),+0s,2299161j)> #Was expecting an error, no arguments has been passed
a = Dia.new(2012, 6, 21, “foo”)
=> TypeError: no implicit conversion to float from string
from (irb):31:in new' from (irb):31 from C:/Ruby193/bin/irb:12:in’ #Seems that the 4th argument is taked by…super too?? WTF
a = Dia.new(2012, 5, 26)
=> #<Dia: 2012-05-26 ((2456074j,0s,0n),+0s,2299161j)>
a = Dia.new(2012, 5, 26, Date::ITALY)
=> #<Dia: 2012-05-26 ((2456074j,0s,0n),+0s,2299161j)> #Obvious is taked by super…but why? I don’t expect that
We can see that new() doesn’t matter if it is no receive parameters, or
if it receive, it behave like make Date.new, but why? I’m re-defining
the method initialize in Dia, it sholud(am I wrong?) take exactly 4
parameters and asign the last one to the instance variable @mes. Why is
this happening? I’ve tried putting super in the first line of the
definition but the same’s returned. Thanks for your time.
class Dia < Date
def initialize
#@mes = obj_mes #super(ano, mes, dia)
puts ‘init’
end
end
Dia.new
–output:–
So that means Dia#initialize is not being called by Dia.new, which is a
bit confounding. Apparently, the date module does some aliasing
which causes new() (which Dia inherits) to call Date#initialize.
Your subclassing of Date problem was discussed in 2001, by none other
than Matz, and supposedly that behavior was going to be fixed:
Well, the class Dia(It’s day in spanish) represent a day. Each instance
of this class have like 10 inst. variables. I wanted to subclass Date
because I want to be available +() or -() or cweek() to a Dia instance,
in the way that it behave like a Date object does.
You can use composition instead of subclassing, as in
require ‘date’
class Dia
def initialize(ano, mes, dia, obj_mes)
@mes=obj_mes @d = Date.new(ano,mes,dia)
end
def print()
printf "date = %04d-%02d-%02d : obj_mes = %-s\n ", @d.year, @d.month, @d.day, @mes
end
end
On Thu, Sep 27, 2012 at 2:30 PM, Damin M. Gonzlez [email protected] wrote:
Why are you subclassing Date in the first place?
Well, the class Dia(It’s day in spanish) represent a day. Each instance
of this class have like 10 inst. variables. I wanted to subclass Date
because I want to be available +() or -() or cweek() to a Dia instance,
in the way that it behave like a Date object does.
Then better use composition as has been suggested. Inheriting core
classes is rarely a good idea. What you have is actually something
else which happens to have a data attached to it as well. If you need
numeric operations one of my blog articles might help you to implement
operators properly:
