# Could not understand this: 3.class is Fixnum or Class

**URL:** <https://www.ruby-forum.com/t/could-not-understand-this-3-class-is-fixnum-or-class/157078>\
**Category:** Ruby\
**Created:** [January 7, 2009, 6:58am UTC](https://www.ruby-forum.com/t/could-not-understand-this-3-class-is-fixnum-or-class/157078 "2009-01-07T06:58:24Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![sentinel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@sentinel](https://www.ruby-forum.com/u/sentinel)\
**Post date:** [January 7, 2009, 6:58am UTC](https://www.ruby-forum.com/t/could-not-understand-this-3-class-is-fixnum-or-class/157078/1 "2009-01-07T06:58:24Z")

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I stored the class of a variable in a variable and later checked in a  
switch-case. Instead of going into the Fixnum case, it goes into ELSE.

c=23.class # =\> Fixnum

c == Fixnum # =\> true

case c; when Fixnum; puts “YES”; else; puts “NO”; end

# =\> prints NO

# after much head-scratching tried this:

case c; when Fixnum; puts “YES”; when Class; puts “CLASS”; else; puts  
“NO”; end

# prints CLASS

* * *

As a result of this I had to store the class as a string (to\_s), so the  
case could work.  
Could someone explain what I am missing here.  
Thx.

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**Author:** ![sentinel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@sentinel](https://www.ruby-forum.com/u/sentinel)\
**Post date:** [January 7, 2009, 8:57am UTC](https://www.ruby-forum.com/t/could-not-understand-this-3-class-is-fixnum-or-class/157078/2 "2009-01-07T08:57:47Z")

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From: Ruby R. [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)]

# c=23.class # =\> Fixnum

# c == Fixnum # =\> true

# case c; when Fixnum; puts “YES”; else; puts “NO”; end

# 

# # =\> prints NO

# # after much head-scratching tried this:

# 

# case c; when Fixnum; puts “YES”; when Class; puts “CLASS”; else; puts

# “NO”; end

# # prints CLASS

case uses ===; thus on your case, it should be easier…

eg try,

> c=23  
> =\> 23

> case c; when Fixnum; puts “YES”; else; puts “NO”; end

YES  
=\> nil

> c=“hello”  
> =\> “hello”

> case c; when Fixnum; puts “YES”; when String; puts “YES STRING!”; else; puts “NO”; end

YES STRING!  
=\> nil

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**Author:** ![sentinel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@sentinel](https://www.ruby-forum.com/u/sentinel)\
**Post date:** [January 7, 2009, 9:09am UTC](https://www.ruby-forum.com/t/could-not-understand-this-3-class-is-fixnum-or-class/157078/3 "2009-01-07T09:09:16Z")

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Stefano C. wrote:

> Alle Wednesday 07 January 2009, Ruby R. ha scritto:
> 
> > Could someone explain what I am missing here.  
> > Thx.
> 
> Stefano

Thanks. Actually both replies side step the issue I have at hand.  
I have an incoming variable, I store its class, the variable is  
converted to a string. When the class returns the variable, it converts  
back.

def set\_buffer val  
@datatype = val.class  
@buffer = val.to\_s  
end

def get\_buffer  
case @datatype  
when Fixnum  
return @buffer.to\_i  
etc  
end

Its like the above.

So, instead of saying

@datatype = val.class.to\_s

and later checking for a string, i was trying to store the class and  
check against it.

Thanks for clearing up the confusion.

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**Author:** ![sentinel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@sentinel](https://www.ruby-forum.com/u/sentinel)\
**Post date:** [January 7, 2009, 9:43am UTC](https://www.ruby-forum.com/t/could-not-understand-this-3-class-is-fixnum-or-class/157078/4 "2009-01-07T09:43:30Z")

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Ruby R. wrote:

> Could someone explain what I am missing here.  
> Thx.

Case statements do not use the equality operator (==), they use the  
“relationship operator” (===), which is typically not commutative. Also,  
the value in the “when” part is the left-hand value (not the right-hand  
value, as you might expect).

Futhermore, Class objects (like Fixnum) use Module’s definition of  
“===”, which returns true if the right-hand side is an instance of the  
module or one of its descendents.

Therefore:

irb(main):001:0\> c = 32.class  
=\> Fixnum  
irb(main):002:0\> Fixnum === c  
=\> false  
irb(main):003:0\> Fixnum === Fixnum  
=\> false  
irb(main):004:0\> Fixnum === 23  
=\> true

-Justin

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**Author:** ![sentinel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@sentinel](https://www.ruby-forum.com/u/sentinel)\
**Post date:** [January 7, 2009, 8:59am UTC](https://www.ruby-forum.com/t/could-not-understand-this-3-class-is-fixnum-or-class/157078/5 "2009-01-07T08:59:33Z")

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Alle Wednesday 07 January 2009, Ruby R. ha scritto:

> Could someone explain what I am missing here.  
> Thx.

The case expression uses the === operator of the objects in the “when”  
statements to decide which one needs to be executed. This means that the  
expression

case c  
when Fixnum then puts “YES”  
when Class then puts “CLASS”  
else puts “NO”  
end

is (more or less) equivalent to the following if expression:

if Fixnum === c then puts “YES”  
elsif Class === c then puts “CLASS”  
else puts “NO”  
end

Now, the documentation for Class#=== (since both Fixnum and Class are  
object  
of class Class) states that it returns true if an instance of the class  
or of  
one of its descendents and false otherwise. In other words, cls === obj  
returns true if obj.is\_a?(cls) returns true and false otherwise. In your  
case,  
the object you’re testing © is the class of 23, that is Fixnum. So,  
when  
executing the case expression, ruby does something like this:

Fixnum === c # returns false because c.is\_a?(Fixnum), that is  
# Fixnum.is\_a?(Fixnum) is false  
Class === c # returns true because c.is\_a?(Class), that is  
# Fixnum.is\_a?(Class) is true  
puts “CLASS”

To get what you want, you have two possibilities:

1. use “case 23” instead of “case c”. This way, it will work as you  
expected,  
because 23 is an instance of class Fixnum, so Fixnum === 23 returns true
2. use an if expression instead of a case expression:  
if c.is\_a?(Fixnum) then #…  
elsif c.is\_a?(Class) then #…  
else #…  
end

I hope this helps

Stefano