Hash insertion order preservation in ruby1.9

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Joachim (München)

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Mar 31, 2008, 6:50:53 AM3/31/08
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I am glad to see that ruby1.9.0 preserves hash insertion order.
It will finally allow me to generate human-readable yaml dumps
without ugly workarounds.

Some questions:

(1) Can I rely upon hash insertion order preservation as an approved
new feature of Ruby, without any risk that it may get lost again in
future releases ?

(2) ri1.9 says:
"The order in which you traverse a hash by either key or value
may seem arbitrary, and will generally not be in the insertion order."
Do I understand correctly that this text is outdated ?

If the answer is two times yes, then read on, please:

(3) Would you agree that the almost undocumented yaml/omap
class is obsolete ? Maybe, one should clearly marked it as such,
or even exclude it from 1.9 ??

(4) Once hashes are ordered, new use cases will be found, and
new methods will become useful. I would like to propose the following
new instance methods
Hash#insert_before( existing_key, other_hash )
Hash#insert_after( existing_key, other_hash )
and possibly also
Hash#insert_before( existing_key, key, value )
Hash#insert_after( existing_key, key, value )
to insert new items at well defined locations. My use case, as I
said before, is a hash which is dumped into human-readable yaml.

Regards, Joachim

Radosław Bułat

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Mar 31, 2008, 10:11:27 AM3/31/08
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I think that you should ask on ruby-core list.

--
Radosław Bułat

http://radarek.jogger.pl - mój blog

Robert Dober

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Mar 31, 2008, 12:34:39 PM3/31/08
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2008/3/31 Radosław Bułat <radek...@gmail.com>:

> I think that you should ask on ruby-core list.
yes but with cross posting please I believe that this of common
interest on this list given its history.

Robert


>
> --
> Radosław Bułat
>
> http://radarek.jogger.pl - mój blog
>

--
http://ruby-smalltalk.blogspot.com/

---
Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein

Yukihiro Matsumoto

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Mar 31, 2008, 5:18:51 PM3/31/08
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Hi,

In message "Re: Hash insertion order preservation in ruby1.9"


on Mon, 31 Mar 2008 19:55:12 +0900, Joachim (München) <wut...@web.de> writes:

|I am glad to see that ruby1.9.0 preserves hash insertion order.
|It will finally allow me to generate human-readable yaml dumps
|without ugly workarounds.
|
|Some questions:
|
|(1) Can I rely upon hash insertion order preservation as an approved
|new feature of Ruby, without any risk that it may get lost again in
|future releases ?

For CRuby, yes. For Ruby the language, we have to make up consensus
with other implementations.

matz.

MenTaLguY

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Mar 31, 2008, 5:30:21 PM3/31/08
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On Tue, 1 Apr 2008 06:18:51 +0900, Yukihiro Matsumoto <ma...@ruby-lang.org> wrote:
> |(1) Can I rely upon hash insertion order preservation as an approved
> |new feature of Ruby, without any risk that it may get lost again in
> |future releases ?
>
> For CRuby, yes. For Ruby the language, we have to make up consensus
> with other implementations.

I think it is safe to say it will remain in JRuby as well. The new
behavior has allowed us to optimize hash iteration since it is now
entirely deterministic.

-mental


Evan David Light

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Mar 31, 2008, 5:49:40 PM3/31/08
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Cool! I've seen folks trip themselves up on this using 1.8.6 before
because of an assumption in their mental model of the language. Nice
to see this addressed.

Sent from my iPhone

Nobuyoshi Nakada

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Apr 1, 2008, 9:39:04 PM4/1/08
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Hi,

At Mon, 31 Mar 2008 19:55:12 +0900,
Joachim (München) wrote in [ruby-talk:296442]:


> (4) Once hashes are ordered, new use cases will be found, and
> new methods will become useful. I would like to propose the following
> new instance methods
> Hash#insert_before( existing_key, other_hash )
> Hash#insert_after( existing_key, other_hash )
> and possibly also
> Hash#insert_before( existing_key, key, value )
> Hash#insert_after( existing_key, key, value )
> to insert new items at well defined locations. My use case, as I
> said before, is a hash which is dumped into human-readable yaml.

What do you expect on conflicts?

--
Nobu Nakada

Joachim (München)

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Apr 10, 2008, 7:00:04 AM4/10/08
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Sorry Nobu, I saw your question only today.

I see two possible conflicts:
- existing _key does not exist
- key already exists
Right?

I would raise an exception in both cases.

Rationale:
One could imagine several other ways to resolve conflicts.
I do not think one of them will be widely accepted as the obvious
right thing to do.
Therefore not attempting to reconcile conflicts will cause the least
surprise.

Regards, Joachim

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