# Range#size

**URL:** <https://www.ruby-forum.com/t/range-size/93898>\
**Category:** Ruby\
**Created:** [April 13, 2006, 3:22pm UTC](https://www.ruby-forum.com/t/range-size/93898 "2006-04-13T15:22:04Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![Meinrad\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ecae2f/32.png) [@Meinrad\_R](https://www.ruby-forum.com/u/Meinrad_R)\
**Post date:** [April 13, 2006, 3:22pm UTC](https://www.ruby-forum.com/t/range-size/93898/1 "2006-04-13T15:22:04Z")

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dear list,

does anyone object to adding the method :size to class Range?

class Range  
def size  
max-min+1  
end  
end

i think it’s useful. maybe others too. i’d like to see it added to the  
core.  
here is the test for Range#size in case it’s really added.

def test\_range\_size  
assert\_equal 1, (1…1).size  
assert\_equal 2, (1…2).size  
assert\_equal 3, (1…3).size  
assert\_equal 0, (1…1).size  
assert\_equal 1, (1…2).size  
end

what do you think?  
– henon

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<div class="post-metadata">

**Author:** ![Meinrad\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ecae2f/32.png) [@Meinrad\_R](https://www.ruby-forum.com/u/Meinrad_R)\
**Post date:** [April 13, 2006, 3:28pm UTC](https://www.ruby-forum.com/t/range-size/93898/2 "2006-04-13T15:28:21Z")

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On Apr 13, 2006, at 8:20 AM, Meinrad R. wrote:

> dear list,
> 
> does anyone object to adding the method :size to class Range?
> 
> class Range  
> def size  
> max-min+1  
> end  
> end

The problem with it is that it adds method dependancies to Range:

> > class Range  
> > def size; max - min + 1 end  
> > end  
> > =\> nil
> 
> > (“AA”…“BB”).size  
> > NoMethodError: undefined method `-' for "BB":String from (irb):2:in`size’  
> > from (irb):4  
> > from :0

James Edward G. II

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<div class="post-metadata">

**Author:** ![Meinrad\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ecae2f/32.png) [@Meinrad\_R](https://www.ruby-forum.com/u/Meinrad_R)\
**Post date:** [April 13, 2006, 3:37pm UTC](https://www.ruby-forum.com/t/range-size/93898/3 "2006-04-13T15:37:33Z")

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On 13-Apr-06, at 9:20 AM, Meinrad R. wrote:

> does anyone object to adding the method :size to class Range?

Forgive me for being blunt, but Ranges don’t have a fixed size, so  
how could you possibly measure it accurately? Force class  
implementers to implement not only a #succ method for their objects,  
but also a #range\_size method which would give a formula for  
calculating the size? I mean seriously…

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<div class="post-metadata">

**Author:** ![Meinrad\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ecae2f/32.png) [@Meinrad\_R](https://www.ruby-forum.com/u/Meinrad_R)\
**Post date:** [April 13, 2006, 3:43pm UTC](https://www.ruby-forum.com/t/range-size/93898/4 "2006-04-13T15:43:46Z")

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On Thu, 13 Apr 2006, Meinrad R. wrote:

> i think it’s useful. maybe others too. i’d like to see it added to the core.  
> what do you think?  
> – henon

this has been discussed before. the main issue is that ranges are not  
sequences, but merely endpoints.

consider:

(0.0 … 1.0).size #=\> Infinite, but how to  
compute?

(0.0 … 1).size #=\> ?

(Rational(5,6) … Rational(5,7)).size #=\> ?

infinity = Float::MAX/Float::EPSILON  
(42.0 … infinity).size #=\> Infinite too

a = Gem::Version.new ‘0.1.0’  
b = Gem::Version.new ‘0.42.0’  
(a … b ).size #=\> potentially Infinite

(42 … -1).size #=\> this is a valid range

if ranges are required to be continuous and bounded they become less  
useful.

i think last time someone suggested an entirely new class…

regards.

-a

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<div class="post-metadata">

**Author:** ![Meinrad\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ecae2f/32.png) [@Meinrad\_R](https://www.ruby-forum.com/u/Meinrad_R)\
**Post date:** [April 13, 2006, 5:14pm UTC](https://www.ruby-forum.com/t/range-size/93898/5 "2006-04-13T17:14:11Z")

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Jeremy T. wrote:

> On 13-Apr-06, at 9:20 AM, Meinrad R. wrote:
> 
> > does anyone object to adding the method :size to class Range?
> 
> Forgive me for being blunt, but Ranges don’t have a fixed size, so  
> how could you possibly measure it accurately? Force class  
> implementers to implement not only a #succ method for their objects,  
> but also a #range\_size method which would give a formula for  
> calculating the size? I mean seriously…

You know, it’s not as though all range operations work with all range  
types anyway:

$ irb --simple-prompt

> > (1.0…2.0).each {|x| p x }  
> > TypeError: can’t iterate from Float  
> > from (irb):1:in `each’  
> > from (irb):1

So, what would be wrong with allowing size for object that implement the

- operation and giving an error for those that don’t?

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<div class="post-metadata">

**Author:** ![Meinrad\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ecae2f/32.png) [@Meinrad\_R](https://www.ruby-forum.com/u/Meinrad_R)\
**Post date:** [April 13, 2006, 5:59pm UTC](https://www.ruby-forum.com/t/range-size/93898/6 "2006-04-13T17:59:53Z")

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On 4/13/06, Meinrad R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> dear list,
> 
> does anyone object to adding the method :size to class Range?
> 
> class Range  
> def size  
> max-min+1  
> end  
> end

a range like “a”…“z” would crash with #size !!  
sorry for the noise. was a bad idea of mine.  
please, just ignore it.

– henon

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**Author:** ![Meinrad\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ecae2f/32.png) [@Meinrad\_R](https://www.ruby-forum.com/u/Meinrad_R)\
**Post date:** [April 14, 2006, 8:03pm UTC](https://www.ruby-forum.com/t/range-size/93898/7 "2006-04-14T20:03:28Z")

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Meinrad R. wrote:

> class Range  
> def size  
> max-min+1  
> end  
> end
> 
> i think it’s useful. maybe others too. i’d like to see it added to the core.  
> here is the test for Range#size in case it’s really added.

Use .to\_a.size instead. 🙂

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<div class="post-metadata">

**Author:** ![Meinrad\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ecae2f/32.png) [@Meinrad\_R](https://www.ruby-forum.com/u/Meinrad_R)\
**Post date:** [April 13, 2006, 5:31pm UTC](https://www.ruby-forum.com/t/range-size/93898/8 "2006-04-13T17:31:45Z")

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On Fri, 14 Apr 2006, Jon B. wrote:

> - operation and giving an error for those that don’t?  
> nothing. but try to write it. it’s harder than you might think.

you need to define as something like this:

class Range  
def size  
begin  
first.distance last  
rescue NoMethodError  
begin  
last.distance first  
rescue NoMethodError  
raise NoMethodError, “size”  
end  
end  
end  
end

class Fixnum  
def distance other  
(other - self).abs  
end  
end

class Float  
def distance other  
Float::MAX/Float::MIN # Infinity  
end  
end

in otherwords the endpoints must to the range size checking - otherwise  
the  
Range class would need to know about every class and how to calculate  
sizes  
for all M x N combinations.

if the endpoints calculate it we can easily do

(0 … 1).size

or

(0.0 … 1.0).size

but what about

(0 … 1.0).size

??

how does Range now which endpoint to use as ‘other’? if we use 1.0 it  
works.  
if we use 0 it does not.

it’s easy enough to fix this for only Fixnum and Float using a smart  
coerce -  
but then we have to deal with Rational, Bignum, Complex, String, etc.  
and we  
haven’t even hit user defined types.

i’m not saying there isn’t an elegant solution. but the problem becomes  
evident imediately when one trys to solve the problem generically.

regards.

-a