Overriding "", [], and {}

ruby-talk
1

Is there any way to cause “”, [], and {} to have different behaviors.
I’d like to be able to have {} create OrderedHash’s instead of Hash’s,
but I don’t know how to change this behavior. If I do Hash =
OrderedHash, then Hash.new will create an OrderedHash, but {} still
gives me an old-fashioned hash. If I do

def Hash.new *args
OrderedHash.new *args
end

I get the same results. Is it possible to override these built-in
constructors?

Bill

2

Bill Atkins wrote:

Is there any way to cause “”, , and {} to have different behaviors.
I’d like to be able to have {} create OrderedHash’s instead of Hash’s,
but I don’t know how to change this behavior. If I do Hash =
OrderedHash, then Hash.new will create an OrderedHash, but {} still
gives me an old-fashioned hash. If I do

def Hash.new *args
OrderedHash.new *args
end

I get the same results. Is it possible to override these built-in
constructors?

I thought of something like this three years ago. It’s not possible.
{ x => y } is a Hash no matter what you do.

can be redefined, but only as a method. [1,2,3] will still be a
plain Array.

That help any?

Hal

3

Bill Atkins wrote:

Is there any way to cause “”, , and {} to have different behaviors.
I’d like to be able to have {} create OrderedHash’s instead of Hash’s,
but I don’t know how to change this behavior. If I do Hash =
OrderedHash, then Hash.new will create an OrderedHash, but {} still
gives me an old-fashioned hash.

This isn’t what you’re looking for, but I think it’s the best answer.
Both Array and Hash have a builtin class method, which can be used to
define new Arrays or Hashes.

a = Array[‘goats’, ‘coats’, ‘asymptotes’]
=> [“goats”, “coats”, “asymptotes”]
h = Hash[‘g’ => ‘goats’, ‘c’ => ‘coats’]
=> {“c”=>“coats”, “g”=>“goats”}

You can use the same class method to get away with really clean
definitions of new Array/Hash derivatives. For example, YAML has an
Omap (ordered hash) class:

o = YAML::Omap[‘c’, ‘coats’, ‘g’, ‘goats’]
=> [[“c”, “coats”], [“g”, “goats”]]
o.class
=> YAML::Omap

_why

4

“why the lucky stiff” ruby-talk@whytheluckystiff.net schrieb im
Newsbeitrag news:40AD161F.6070107@whytheluckystiff.net…

Bill Atkins wrote:

Is there any way to cause “”, , and {} to have different behaviors.
I’d like to be able to have {} create OrderedHash’s instead of Hash’s,
but I don’t know how to change this behavior. If I do Hash =
OrderedHash, then Hash.new will create an OrderedHash, but {} still
gives me an old-fashioned hash.

This isn’t what you’re looking for, but I think it’s the best answer.
Both Array and Hash have a builtin class method, which can be used to
define new Arrays or Hashes.

a = Array[‘goats’, ‘coats’, ‘asymptotes’]
=> [“goats”, “coats”, “asymptotes”]
h = Hash[‘g’ => ‘goats’, ‘c’ => ‘coats’]
=> {“c”=>“coats”, “g”=>“goats”}

You can use the same class method to get away with really clean
definitions of new Array/Hash derivatives. For example, YAML has an
Omap (ordered hash) class:

o = YAML::Omap[‘c’, ‘coats’, ‘g’, ‘goats’]
=> [[“c”, “coats”], [“g”, “goats”]]
o.class
=> YAML::Omap

_why

or how about

oh = OrderedHash.new.update( {
“foo” => “bar”,
"bar2 => “foo”,
} )

robert
5

Robert Klemme wrote:

“why the lucky stiff” ruby-talk@whytheluckystiff.net schrieb im
Newsbeitrag news:40AD161F.6070107@whytheluckystiff.net…

o = YAML::Omap[‘c’, ‘coats’, ‘g’, ‘goats’]
=> [[“c”, “coats”], [“g”, “goats”]]
o.class
=> YAML::Omap

_why

or how about

oh = OrderedHash.new.update( {
“foo” => “bar”,
"bar2 => “foo”,
} )

But then the order in the “ordered hash” is not necessarily the same
as that specified in the single hash passed in as a parameter.

Hal

6

“Hal Fulton” hal9000@hypermetrics.com schrieb im Newsbeitrag
news:40AD305C.6030408@hypermetrics.com…

Robert Klemme wrote:

“why the lucky stiff” ruby-talk@whytheluckystiff.net schrieb im
Newsbeitrag news:40AD161F.6070107@whytheluckystiff.net…

o = YAML::Omap[‘c’, ‘coats’, ‘g’, ‘goats’]
=> [[“c”, “coats”], [“g”, “goats”]]
o.class
=> YAML::Omap

_why

or how about

oh = OrderedHash.new.update( {
“foo” => “bar”,
"bar2 => “foo”,
} )

But then the order in the “ordered hash” is not necessarily the same
as that specified in the single hash passed in as a parameter.

My fault, I forgot that OrderedHash maintains insertion order and not some
other order. Sorry, just forget my proposal.

robert