Defining key equivalence in a hash

ruby-talk
1

Hello,

I'm trying to make two keys equivalent by having their #hash method
produce the same result. But this does not seem to work:

irb(main):001:0> class K; def hash; 90; end; end
=> nil
irb(main):002:0> h = {}
=> {}
irb(main):003:0> h[K.new] = 1
=> 1
irb(main):004:0> h.key? K.new # <---- I want this to return true!
=> false

What am I missing?

Thanks for your consideration.

···

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2

If you put K.new into a variable, and then check for that, it will return true:

irb(main):001:0> class K; def hash; 90; end; end
=> nil
irb(main):002:0> h = {}
=> {}
irb(main):003:0> k = K.new
=> #<K:0xb7cac4ac>
irb(main):004:0> h[k] = 1
=> 1
irb(main):005:0> h[k]
=> 1
irb(main):006:0> h.key? k
=> true

It's because K.new creates a new location in memory for each call to it, but h.key? checks the location in memory, not the contents of the keys and the objects passed to it. So if you call K.new twice, each will return a new location in memory.

Dan

Suraj Kurapati wrote:

···

Hello,

I'm trying to make two keys equivalent by having their #hash method
produce the same result. But this does not seem to work:

irb(main):001:0> class K; def hash; 90; end; end
=> nil
irb(main):002:0> h = {}
=> {}
irb(main):003:0> h[K.new] = 1
=> 1
irb(main):004:0> h.key? K.new # <---- I want this to return true!
=> false

What am I missing?

Thanks for your consideration.

3

class K; def eql?(other) true; end; end

#eql? is called if o1.hash == o2.hash. If #eql? returns true the objects belong to the same index.

···

On Dec 10, 2006, at 11:33 , Suraj Kurapati wrote:

Hello,

I'm trying to make two keys equivalent by having their #hash method
produce the same result. But this does not seem to work:

irb(main):001:0> class K; def hash; 90; end; end
=> nil
irb(main):002:0> h = {}
=> {}
irb(main):003:0> h[K.new] = 1
=> 1
irb(main):004:0> h.key? K.new # <---- I want this to return true!
=> false

What am I missing?

--
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net

I LIT YOUR GEM ON FIRE!

4

K#eql?

for example

   harp:~ > cat a.rb
   class K
     attr 'key'
     def initialize() @key = 42 end
     def hash() @key.hash end
     def eql?(other) other.key == @key end
   end

   p K.new => 'which', K.new => 'one'

   harp:~ > ruby a.rb
   {#<K:0xb75cca34 @key=42>=>"one"}

regards.

-a

···

On Mon, 11 Dec 2006, Suraj Kurapati wrote:

Hello,

I'm trying to make two keys equivalent by having their #hash method
produce the same result. But this does not seem to work:

irb(main):001:0> class K; def hash; 90; end; end
=> nil
irb(main):002:0> h = {}
=> {}
irb(main):003:0> h[K.new] = 1
=> 1
irb(main):004:0> h.key? K.new # <---- I want this to return true!
=> false

What am I missing?

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if you want to be happy, practice compassion. -- the dalai lama