From: Nikolai Weibull <now@...>
Date: 2011-12-30T18:09:01+09:00
Subject: Re: What’s the standard way of implementing #hash for value objects in Ruby?

On Fri, Dec 30, 2011 at 06:25, Josh Cheek <josh.cheek@gmail.com> wrote:
> On Thu, Dec 29, 2011 at 5:47 PM, Nikolai Weibull <now@bitwi.se> wrote:
>> So, again, what’s the standard way of implementing #hash for value objects in Ruby?

> If there is one, I don't know what it is, which implies there isn't one.

That’s a very bold statement to make, considering that you don’t seem
to know how #hash should be implemented:

> I usually just delegate to one of my attributes' hash methods (e.g. for a
> user, I might use its user's name's hash). I'm not sure what advantage
> would be gained by establishing a standard.

If there was a standard way, then no one would have to ask if there
was one.  It would make implementing #hash, which you should/must do
if you implement #==, trivial, as there’s then only one way to do so.
It would make hashing conflicts less likely, as the correct set of
parameters would be used, whatever the object, and a uniform
distribution could be established across different classes of objects.

Perhaps Ruby’s internal hashing functions (rb_hash_start,
rb_hash_uint, rb_hash_end) could be exposed in some new object?

Note that these functions are currently not being used in a uniform
way internally.  For example, Struct starts with the #hash of the
object’s class, while Array starts with #length.