ruby, even? and odd? methods in Integer class

kwat
#1 / 7

even? and odd? methods in Integer class

Why Integer class doesn't have 'even?' nor 'odd?' method?
Of course, it is easy to define by myself.
But I wonder why these methods are not included in Ruby
by default?

.--------------------
class Integer
def even?
return self % 2 == 0
end
def odd?
return self % 1 == 0
end
end
.--------------------

I believe that these methods are very useful and friendly,
especially for Web Designers.
They're familiar with a concept about modulo, but not familiar
with an operator of modulo (= '%').

.--------------------
<% count = 0 %>
<% for item in list do %>
<% count += 1 %>
<% if count % 2 == 0 then %> 
<tr class="even">
<td><%=item%></td>
</tr>
<% else %>
<tr class="odd">
<td><%=item%></td>
</tr>
<% end %>
<% end %>
.--------------------

I hope these methods are to be built-in methods.
Give your opinion, please.

--
regards
kwatch

Fri, 05 Aug 2005 17:47:48 GMT

Mike Wye
#2 / 7

even? and odd? methods in Integer class

Quote:

> Why Integer class doesn't have 'even?' nor 'odd?' method?
> Of course, it is easy to define by myself.
> But I wonder why these methods are not included in Ruby
> by default?

> ..--------------------
> class Integer
> def even?
> return self % 2 == 0
> end
> def odd?
> return self % 1 == 0
> end
> end
> ..--------------------

> I believe that these methods are very useful and friendly,
> especially for Web Designers.
> They're familiar with a concept about modulo, but not familiar
> with an operator of modulo (= '%').

> ..--------------------
> <% count = 0 %>
> <% for item in list do %>
> <% count += 1 %>
> <% if count % 2 == 0 then %> 
> <tr class="even">
> <td><%=item%></td>
> </tr>
> <% else %>
> <tr class="odd">
> <td><%=item%></td>
> </tr>
> <% end %>
> <% end %>
> ..--------------------

> I hope these methods are to be built-in methods.
> Give your opinion, please.

Your odd? definition returns true for all ints.
All integers are 0 modulo 1.

You want self % 2 == 1:

irb(main):001:0> class Integer
irb(main):002:1> def odd?
irb(main):003:2> self % 1 == 0
irb(main):004:2> end
irb(main):005:1> end
nil
irb(main):006:0> 3.odd?
true
irb(main):007:0> 4.odd?
true
irb(main):008:0> class Integer
irb(main):009:1> def odd?
irb(main):010:2> self % 2 == 1
irb(main):011:2> end
irb(main):012:1> end
nil
irb(main):013:0> 3.odd?
true
irb(main):014:0> 4.odd?
false

Cheers,
Mike
--

"I want to die peacefully in my sleep like my Grandfather...
... not screaming and yelling like the passengers in his car"

Fri, 05 Aug 2005 21:47:00 GMT

Warren Brow
#3 / 7

even? and odd? methods in Integer class

kwatch,

Quote:

> Why Integer class doesn't have 'even?' nor 'odd?' method?
> Of course, it is easy to define by myself.
> But I wonder why these methods are not included in Ruby
> by default?

> ..--------------------
> class Integer
> def even?
> return self % 2 == 0
> end
> def odd?
> return self % 1 == 0
> end
> end
> ..--------------------

I don't know why these methods are not predefined, but there is a
simpler (and presumably faster) check for even and odd. I use "mynumber[0]
== 0" to check for even and "mynumber[0] == 1" to check for odd. It is
trivial to add these to the Integer class (which may be why these are not
predefined):

class Integer
def even?() self.[](0) == 0 end
del odd?() self.[](0) == 1 end
end

So:

1.even? => false
1.odd? => true

Hope this helps!

- Warren Brown

Sat, 06 Aug 2005 00:30:54 GMT

Hal E. Fulto
#4 / 7

even? and odd? methods in Integer class

Quote:

----- Original Message -----

Newsgroups: comp.lang.ruby

Sent: Monday, February 17, 2003 4:04 AM
Subject: even? and odd? methods in Integer class

> Why Integer class doesn't have 'even?' nor 'odd?' method?
> Of course, it is easy to define by myself.
> But I wonder why these methods are not included in Ruby
> by default?

Frankly, I would like to see this (at least odd?
since even? is just the opposite -- Pascal went
this route -- but I am showing my age when I
mention that).

It's been discussed before, but I think Matz said
it was not needed often enough and/or was very
simple to implement anyway.

Of course, there are other more general choices
you could make also.

count.mult?(n) # is count a multiple of n?
count.mod?(5,2) # is count mod 5 equal to 2?

The latter mod? method could have the second param
default to zero, so that it included the function
of mult? also.

Cheers,
Hal

Sat, 06 Aug 2005 05:43:08 GMT

kwat
#5 / 7

even? and odd? methods in Integer class

Quote:

> Your odd? definition returns true for all ints.
> All integers are 0 modulo 1.

> You want self % 2 == 1:

Oh, sorry, you're right.
It's my mistake.

kwatch

Sat, 06 Aug 2005 11:01:54 GMT

kwat
#6 / 7

even? and odd? methods in Integer class

Quote:

> Frankly, I would like to see this (at least odd?
> since even? is just the opposite -- Pascal went
> this route -- but I am showing my age when I
> mention that).

I know pascal, not delphi.
I'm showing my age, too.

Quote:

> It's been discussed before, but I think Matz said
> it was not needed often enough and/or was very
> simple to implement anyway.

> Of course, there are other more general choices
> you could make also.

> count.mult?(n) # is count a multiple of n?
> count.mod?(5,2) # is count mod 5 equal to 2?

> The latter mod? method could have the second param
> default to zero, so that it included the function
> of mult? also.

> Cheers,
> Hal

Oh, it is right.
I must define if I want, and I can do.
Thanks Hal.

--
regards,
kwatch

Sun, 07 Aug 2005 03:37:20 GMT

Martin DeMell
#7 / 7

even? and odd? methods in Integer class

Quote:

> I don't know why these methods are not predefined, but there is a
> simpler (and presumably faster) check for even and odd. I use "mynumber[0]
> == 0" to check for even and "mynumber[0] == 1" to check for odd. It is
> trivial to add these to the Integer class (which may be why these are not
> predefined):

Neat! Never knew about Integer#[]

martin

Thu, 11 Aug 2005 04:22:12 GMT