Valid hash keys

ruby-talk
1

unlike perl, ruby treats 1 and ‘1’ differently in hash keys:

$ irb
irb(main):001:0> a={}
irb(main):002:0> a[1]=1
irb(main):003:0> a[‘1’]='1’
irb(main):004:0> a
{1=>1, “1”=>“1”}

so what are the range the valid values for hash keys? can i, like in
python, use “immutable lists”/tuples as hash keys?

···

–
dave

2

unlike perl, ruby treats 1 and ‘1’ differently in hash keys:

This is largely because:

  • Perl will happily change numbers to strings (and back), sometimes
    when you’re least expecting it.

  • Perl only uses strings as hash keys.

so what are the range the valid values for hash keys? can i, like
in python, use “immutable lists”/tuples as hash keys?

You can use any object.

$ ri Object.hash

···

On Saturday 20 July 2002 09:07 am, David Garamond wrote:

Object#hash
obj.hash → aFixnum

 Generates a Fixnum hash value for this object. This function must
 have the property that a.eql?(b) implies a.hash == b.hash. The

hash
value is used by class Hash. Any hash value that exceeds the
capacity of a Fixnum will be truncated before being used.

–
Ned Konz
http://bike-nomad.com
GPG key ID: BEEA7EFE

3

“David Garamond” davegaramond@icqmail.com wrote in message
news:3D398A76.8090504@icqmail.com…

so what are the range the valid values for hash keys? can i, like in
python, use “immutable lists”/tuples as hash keys?

As Ned Konz has already replied, you can use any object as a hash key since
they all respond to the “hash” message. But since Ruby arrays (and strings,
for that matter) aren’t immutable you want to be careful about using them as
hash keys. Specifically, if you use a mutable object as a hash key and then
change its value, be sure to call rehash on the Hash object. See this page
from “Programming Ruby”:

http://www.rubycentral.com/book/ref_c_hash.html#Hash.rehash

for a short and sweet example.