Class X < Hash ... how do I do X.new { |hash, key| ...}?

Ruby
1

I created a child class of Hash and would like to internalize the
equivalent of Hash.new {|hash,key| } The following code failed:

class X < Hash
def initialize
super { |hash,key| … }
end
end

Any suggestions? I suppose I could do it externally with a create()
wrapper but it doesn’t seem very pragmatic.

def create_X
y = X.new {|hash,key| … }
return y
end

My overall goal is to record a list of attempts to read undefined Keys.

Thanks,
Larry

2

Hi –

On Sun, 26 Aug 2007, Larry F. wrote:

wrapper but it doesn’t seem very pragmatic.

def create_X
y = X.new {|hash,key| … }
return y
end

My overall goal is to record a list of attempts to read undefined Keys.

Here’s what I did – I’m not sure how it differs from yours but
hopefully it will help:

class X < Hash
attr_accessor :attempts
def initialize
self.attempts = []
super {|h,k| attempts << k unless h.has_key?(k); nil }
end
end

h = X.new
h[1] = 2
p h[1] # 2
p h[0] # nil
p h[2] # nil
p h.attempts # [0,2]

David

3

Hi,

Am Sonntag, 26. Aug 2007, 09:06:24 +0900 schrieb Larry F.:

I created a child class of Hash and would like to internalize the
equivalent of Hash.new {|hash,key| } The following code failed:

class X < Hash
def initialize
super { |hash,key| … }
end
end

Any suggestions?

Any error messages?

I pipe the following code from here in the editor into Ruby:

class H < Hash
def initialize
super { |h,k| h[k] = Time.now }
end
end
h = H.new
puts h[:x]
sleep 1
puts h[:y]
puts h[:x]

Sun Aug 26 02:30:35 +0200 2007
Sun Aug 26 02:30:36 +0200 2007
Sun Aug 26 02:30:35 +0200 2007

Bertram

4

Thank you both. Yes, that works. So I’m puzzled by the error I was
getting. Oh well, carrying on…

I still have a related problem. I’m using YML to export and import my
Hash. YML loses all the Hash initialization settings. So I may still
have to create a new internal Hash after reloading from YML.

class X < Hash
attr_accessor :attempts
def initialize
self.attempts = []
super {|h,k| attempts << k unless h.has_key?(k); nil }
end
end

h = X.new
h[1] = 2
p h[1] # 2
p h[0] # nil
p h[2] # nil
p h.attempts # [0,2]

yml_text = YAML.dump(h) # “— !map:X \n1: 2\n”
j = YAML.load(yml_text) # {1=>2}
j.class # X
j.attempts # nil
j[2] = 25 # 25
j # {1=>2, 2=>25}
j[3] # nil
j.attempts # nil