Hash order bug?

ruby-talk
1

No, it's just the way hashes behave. Note that there are ordered hash
implementations on the RAA:

http://raa.ruby-lang.org/project/orderedhash/

You can also use a Struct to get roughly the same effect.

Regards,

Dan

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ยทยทยท

-----Original Message-----
From: Javier Valencia [mailto:jvalencia@log01.org]
Sent: Tuesday, July 25, 2006 7:48 AM
To: ruby-talk ML
Subject: Re: Hash order bug?

dblack@wobblini.net wrote:

> Hi --
>
> On Tue, 25 Jul 2006, Javier Valencia wrote:
>
>> I have this piece of simple code:
>>
>> ----------------------------------------------
>> def foo
>> return 5
>> end
>>
>> a = {:gr => false, :und => false, :det => true, :sta => false, :inv
>> => false}
>> puts a.inspect
>> ----------------------------------------------
>>
>> when I execute it i get a totally unordered hash:
>>
>> ----------------------------------------------
>> ruby pro.rb
>> {:inv=>false, :gr=>false, :und=>false, :det=>true, :sta=>false}
>> ----------------------------------------------
>>
>> Now, i delete the foo function from the code (the foo
function don't
>> do nothing at all), and i get a well ordered hash:
>>
>> ----------------------------------------------
>> ruby pro.rb
>> {:gr=>false, :und=>false, :det=>true, :sta=>false, :inv=>false}
>> ----------------------------------------------
>>
>>
>> What's happening? all my code is behaving wrong because of that.
>
>
> Hashes are unordered. If you need an ordered collection,
you'll need
> to use an array.
>
>
> David
>

Oh my god, i didn't know it, sorry. Is that a missing feature?

2

Berger, Daniel wrote:

No, it's just the way hashes behave. Note that there are ordered hash
implementations on the RAA:

http://raa.ruby-lang.org/project/orderedhash/

You can also use a Struct to get roughly the same effect.

In case anyone tries to refer me to these, I'll point out that
there are *three* reasons I like a hash.

1. It indexes on an arbitrary value, not on an integer like
an array.
2. It consists of explicit pairings of key and value.
3. There is a convenient sybtax for literals:
    {a=>b, c=>d, e=>f}

Note that there are *no* ordered hash solutions that preserve
the third criterion.

Most would require me to do something like:

   oh = OrdHash.new(a,b, c,d, e,f)

or

   oh = OrdHash.new([a,b], [c,d], [e,f])

or something just as bad.

Don't underestimate the importance of a convenient notation!
What if arrays in Ruby were like arrays in C? In C, you can
specify an array literal (barely) when you declare it; that's
about it.

Hal