Creating object from hash

ruby-talk
1

I'm creating an object from a hash using this:

class Computer
  def initialize(hash)
    hash.each do |k,v|
      instance_variable_set("@#{k}", v) ## create and initialize an
instance variable for this key/value pair
      instance_eval %Q{ class << self ; attr_reader #{k.intern.inspect}
; end }
    end
  end
end

This works fine except if I need to define a method with the same name
of a key (if I need an complicated getter/setter for example). So I
added a test to attr_reader line:
instance_eval %Q{ class << self ; attr_reader #{k.intern.inspect} ; end
} if !instance_eval %Q{defined? #{k}}

As an Object, some methods are defined (like "id"). So "pc =
Computer.new({'id' > 1})" does not create the reader for @id and "pc.id"
calls some unwanted method.

If I just add "attr_reader :id" everything works. Can I do it directly,
without adding attr_reader (or attr_accessor) every time that I get an
error?

···

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2

Hi,

I'm creating an object from a hash using this:

class Computer
def initialize(hash)
   hash.each do |k,v|
     instance_variable_set("@#{k}", v) ## create and initialize an
instance variable for this key/value pair
     instance_eval %Q{ class << self ; attr_reader #{k.intern.inspect}
; end }
   end
end
end

Just wondering if you've looked at OpenStruct?

   % ri OpenStruct

You can achieve the above more simply.

   require 'ostruct'
   Computer = Class.new(OpenStruct) # or class Computer < OpenStruct ...

This works fine except if I need to define a method with the same name
of a key (if I need an complicated getter/setter for example). So I
added a test to attr_reader line:
instance_eval %Q{ class << self ; attr_reader #{k.intern.inspect} ; end
} if !instance_eval %Q{defined? #{k}}

As an Object, some methods are defined (like "id"). So "pc =
Computer.new({'id' > 1})" does not create the reader for @id and "pc.id"
calls some unwanted method.

"id" is technically deprecated. Even so, it's also available at Object#__id__ and Object#object_id.

But still, you can undefine methods:

% ri Module#undef_method

If I just add "attr_reader :id" everything works. Can I do it directly,
without adding attr_reader (or attr_accessor) every time that I get an
error?

Try some of the things I've mentioned above?

Best,
Stephen

···

On Nov 6, 2008, at 2:44 PM, Davi Barbosa wrote:

3

You can make your life easier with Struct:

irb(main):001:0> Comp = Struct.new :id do
irb(main):002:1* def initialize(h)
irb(main):003:2> members.each {|m| self[m] = h[m] || h[m.to_sym]}
irb(main):004:2> end
irb(main):005:1> end
=> Comp
irb(main):006:0> c = Comp.new(:id=>133)
=> #<struct Comp id=133>
irb(main):007:0> d = Comp.new("id"=>133)
=> #<struct Comp id=133>
irb(main):008:0>

Kind regards

  robert

···

On 06.11.2008 21:44, Davi Barbosa wrote:

I'm creating an object from a hash using this:

class Computer
  def initialize(hash)
    hash.each do |k,v|
      instance_variable_set("@#{k}", v) ## create and initialize an
instance variable for this key/value pair
      instance_eval %Q{ class << self ; attr_reader #{k.intern.inspect}
; end }
    end
  end
end

This works fine except if I need to define a method with the same name
of a key (if I need an complicated getter/setter for example). So I
added a test to attr_reader line:
instance_eval %Q{ class << self ; attr_reader #{k.intern.inspect} ; end
} if !instance_eval %Q{defined? #{k}}

As an Object, some methods are defined (like "id"). So "pc =
Computer.new({'id' > 1})" does not create the reader for @id and "pc.id"
calls some unwanted method.

If I just add "attr_reader :id" everything works. Can I do it directly,
without adding attr_reader (or attr_accessor) every time that I get an
error?

4

and even easier with fattr

class Computer
   fattr :foo
   fattr :bar

   def initialize options = {}
     options.each{|k,v| send k, v}
   end
end

a @ http://codeforpeople.com/

···

On Nov 6, 2008, at 4:03 PM, Robert Klemme wrote:

On 06.11.2008 21:44, Davi Barbosa wrote:

I'm creating an object from a hash using this:
class Computer
def initialize(hash)
   hash.each do |k,v|
     instance_variable_set("@#{k}", v) ## create and initialize an
instance variable for this key/value pair
     instance_eval %Q{ class << self ; attr_reader #{k.intern.inspect}
; end }
   end
end
end
This works fine except if I need to define a method with the same name
of a key (if I need an complicated getter/setter for example). So I
added a test to attr_reader line:
instance_eval %Q{ class << self ; attr_reader #{k.intern.inspect} ; end
} if !instance_eval %Q{defined? #{k}}
As an Object, some methods are defined (like "id"). So "pc =
Computer.new({'id' > 1})" does not create the reader for @id and "pc.id"
calls some unwanted method.
If I just add "attr_reader :id" everything works. Can I do it directly,
without adding attr_reader (or attr_accessor) every time that I get an
error?

You can make your life easier with Struct:

irb(main):001:0> Comp = Struct.new :id do
irb(main):002:1* def initialize(h)
irb(main):003:2> members.each {|m| self[m] = h[m] || h[m.to_sym]}
irb(main):004:2> end
irb(main):005:1> end
=> Comp
irb(main):006:0> c = Comp.new(:id=>133)
=> #<struct Comp id=133>
irb(main):007:0> d = Comp.new("id"=>133)
=> #<struct Comp id=133>
irb(main):008:0>

Kind regards

  robert

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