How come this code doesn't return "true" for the following?
x = [1,2,3]
puts(x.include?(Fixnum))
Thanks
···
--
Posted via http://www.ruby-forum.com/.
It uses ==, not ===.
$ri Enumerable#include?
---------------------------------------------------- Enumerable#include?
enum.include?(obj) => true or false
enum.member?(obj) => true or false
···
On Jan 4, 2008 9:05 AM, Sam Phoneix <dominicjefferies@yahoo.co.uk> wrote:
How come this code doesn't return "true" for the following?
x = [1,2,3]
puts(x.include?(Fixnum))
------------------------------------------------------------------------
Returns +true+ if any member of _enum_ equals _obj_. Equality is
tested using +==+.
Sam Phoneix wrote:
How come this code doesn't return "true" for the following?
x = [1,2,3]
puts(x.include?(Fixnum))
Thanks
Because include? doesn't test the class of an object, it tests for the presence of an object. The ri command is your friend here:
$ ri Array.include?
--------------------------------------------------------- Array#include?
array.include?(obj) -> true or false
···
------------------------------------------------------------------------
Returns true if the given object is present in self (that is, if
any object == anObject), false otherwise.
a = [ "a", "b", "c" ]
a.include?("b") #=> true
a.include?("z") #=> false
--
RMagick: http://rmagick.rubyforge.org/
RMagick 2: http://rmagick.rubyforge.org/rmagick2.html
You could try something like:
class Array
def include_class?(klass)
if self.detect { |x| x.class == klass }
return true
else
return false
end
end
end
···
On Jan 4, 2008 4:05 PM, Sam Phoneix <dominicjefferies@yahoo.co.uk> wrote:
How come this code doesn't return "true" for the following?
x = [1,2,3]
puts(x.include?(Fixnum))
How come this code doesn't return "true" for the following?
x = [1,2,3]
puts(x.include?(Fixnum))
In addition to the reasons other people mentioned, Fixnum is an actual
object in Ruby. You could put it in an array if you wanted:
classes_that_start_with_f = [Fixnum, File, FizzBuzz]
classes_that_start_with_f.include?(Fixnum) # returns true
That's why it doesn't work like you expect; because #include?(Fixnum)
is for finding the actual Fixnum class object.
To get what you want the best approach is map, or one of a few
functions similar to map, such as collect or inject:
[1,2,3].map {|number| number.is_a? Fixnum}
=> [true, true, true]
[1,2,3,"asdfasdfasdf"].map {|number| number.is_a? Fixnum}
=> [true, true, true, false]
[1,2,3,"asdfasdfasdf"].map {|number| number.is_a? Fixnum}.include?(true)
=> true
class Array
def include_class?(klass)
map do |thing|
thing.is_a? klass
end.include?(true)
end
end
[1,2,3].include_class?(Fixnum)
=> true
Thomas Wieczorek's solution is good too. #detect is a cousin of #map.
···
--
Giles Bowkett
Podcast: http://hollywoodgrit.blogspot.com
Blog: http://gilesbowkett.blogspot.com
Portfolio: http://www.gilesgoatboy.org
Tumblelog: http://giles.tumblr.com
Giles Bowkett wrote:
[1,2,3].map {|number| number.is_a? Fixnum}
=> [true, true, true]
Thanks
···
--
Posted via http://www.ruby-forum.com/\.
Well, if you're trying to find out if the array contains at least one
Fixnum then this isn't really the best way. Instead I'd use
x.any? {|obj| Fixnum === obj }
which returns a single boolean, and only looks at as many elements of
the array as it needs to.
Alternately one could use
x.find {|obj| Fixnum === obj }
which will return either the first Fixnum in the array, or nil if
their isn't one, which can be used the same way as a boolean value in
almost all cases.
···
On Jan 4, 2008 11:25 AM, Giles Bowkett <gilesb@gmail.com> wrote:
> How come this code doesn't return "true" for the following?
>
> x = [1,2,3]
>
> puts(x.include?(Fixnum))
To get what you want the best approach is map, or one of a few
functions similar to map, such as collect or inject:
--
Rick DeNatale
My blog on Ruby
http://talklikeaduck.denhaven2.com/
Well, if you're trying to find out if the array contains at least one
Fixnum then this isn't really the best way. Instead I'd usex.any? {|obj| Fixnum === obj }
which returns a single boolean, and only looks at as many elements of
the array as it needs to.
Yeah, I think that's the best way too.
···
--
Giles Bowkett
Podcast: http://hollywoodgrit.blogspot.com
Blog: http://gilesbowkett.blogspot.com
Portfolio: http://www.gilesgoatboy.org
Tumblelog: http://giles.tumblr.com
> Well, if you're trying to find out if the array contains at least one
> Fixnum then this isn't really the best way. Instead I'd use
>
> x.any? {|obj| Fixnum === obj }
>
> which returns a single boolean, and only looks at as many elements of
> the array as it needs to.Yeah, I think that's the best way too.
Wait, no I don't. I'd say switch === with .is_a? and that would be the
best way. More readable, and allows you to avoid the question "what is
===?"
Generally I think you should avoid === unless implementing it on new
classes for the sake of case/switch statements.
···
--
Giles Bowkett
Podcast: http://hollywoodgrit.blogspot.com
Blog: http://gilesbowkett.blogspot.com
Portfolio: http://www.gilesgoatboy.org
Tumblelog: http://giles.tumblr.com