From: Ryan Davis <ryand-ruby@...>
Date: 2010-01-07T07:07:02+09:00
Subject: Re: what's String.hash


On Jan 5, 2010, at 18:56 , Ruby Newbee wrote:

> irb(main):038:0* x="hello"
> => "hello"
> irb(main):039:0> x.object_id
> => 69352346
> irb(main):040:0> x.hash
> => 267522041
> irb(main):041:0> y="hello".intern
> => :hello
> irb(main):042:0> y.object_id
> => 246184
> irb(main):043:0> y.hash
> => 246184
> 
> 
> What's the meanings of String.hash method?
> does it have any relation to object_id? Thanks.

You should be using ri to answer these questions:

501 % ri String.hash
------------------------------------------------------------ String#hash
     str.hash   => fixnum

     From Ruby 1.8
------------------------------------------------------------------------
     Return a hash based on the string's length and content.

502 % ri Object.hash
------------------------------------------------------------ Object#hash
     obj.hash    => fixnum

     From Ruby 1.8
------------------------------------------------------------------------
     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.

503 % ri Object.object_id
------------------------------------------------------- Object#object_id
     obj.__id__       => fixnum
     obj.object_id    => fixnum

     From Ruby 1.8
------------------------------------------------------------------------
     Returns an integer identifier for _obj_. The same number will be
     returned on all calls to +id+ for a given object, and no two active
     objects will share an id. +Object#object_id+ is a different concept
     from the +:name+ notation, which returns the symbol id of +name+.
     Replaces the deprecated +Object#id+.