Hi all,
I am new to Ruby and am trying to overload “+” operator on Integer
class, without success.
class TestNum < Integer
def +(other)
self.value - other
end
end
puts TestNum.new(5)+5; # should return 0
I know that it should be simple, but… any help appreciated.
Bojan M. wrote:
puts TestNum.new(5)+5; # should return 0
I know that it should be simple, but… any help appreciated.
Did you look at the error?
?> TestNum.new(5)+5
NoMethodError: undefined method `new’ for TestNum:Class
from (irb):7
from :0
Your problem starts already with the creation… Integer is an abstract
class and I suspect it does something to #new.
You should also look at #coerce, see
http://www.rubygarden.org/ruby?CoerceExplanation for example if you want
to implement operators properly.
Kind regards
robert
On Jan 6, 2006, at 10:35 AM, Bojan M. wrote:
puts TestNum.new(5)+5; # should return 0
I know that it should be simple, but… any help appreciated.
Ruby provides the coerce method, for hooking into its math routines:
class TestNum
def initialize( value )
@value = value
end
attr_reader :value
def +( other )
if other.is_a? self.class
value + other.value
else
?> value + other
end
end
def coerce( other )
[self.class.new(other), self]
end
end
=> nil
tn = TestNum.new(5)
=> #<TestNum:0x31d2b8 @value=5>
tn + 5
=> 10
tn + tn
=> 10
5 + tn
=> 10
Hope that helps.
James Edward G. II
Thanks James. As I understand coerce method in Ruby classes is to assure
‘other’ is of right type and that operation could be performed. In this
example coerce is called from FixNum class, and ‘+’ method is always
preformed in TestNum class, right?
On Jan 6, 2006, at 12:57 PM, Bojan M. wrote:
Thanks James. As I understand coerce method in Ruby classes is to
assure ‘other’ is of right type and that operation could be
performed. In this example coerce is called from FixNum class, and
‘+’ method is always preformed in TestNum class, right?
Yes, that’s correct.
James Edward G. II