Dynamic class instantiation by iteration

ruby-talk
1

I'm curious as to why the following does not create three instances of
class Cat:

class Cat
   def initialize(name)
      @name = name
   end
end

toons = ["Felix", "Garfield", "Heathcliff"]

toons.each {|t| t = Cat.new(t)}

In irb, the last input and output are:

irb(main):008:0> toons.each {|t| t=Cat.new(t)}
=> ["Felix", "Garfield", "Heathcliff"]

which I don't understand.

2

Your code does create three instances of Cat, but they're thrown away
immediately, since you don't use them. Array#each always return the receiver
(in your case, the array ["Felix", "Garfield", "Heathcliff"]), regardless of
the return value of the block. If you want to obtain an array with the three
instances of Cat, use Array#map instead:

cats = toons.map{|n| Cat.new(name)}

I hope this helps

Stefano

···

On Wednesday 30 April 2008, Frisco Del Rosario wrote:

I'm curious as to why the following does not create three instances of
class Cat:

class Cat
   def initialize(name)
      @name = name
   end
end

toons = ["Felix", "Garfield", "Heathcliff"]

toons.each {|t| t = Cat.new(t)}

In irb, the last input and output are:

irb(main):008:0> toons.each {|t| t=Cat.new(t)}
=> ["Felix", "Garfield", "Heathcliff"]

which I don't understand.

3

Hi --

···

On Wed, 30 Apr 2008, Stefano Crocco wrote:

On Wednesday 30 April 2008, Frisco Del Rosario wrote:

I'm curious as to why the following does not create three instances of
class Cat:

class Cat
   def initialize(name)
      @name = name
   end
end

toons = ["Felix", "Garfield", "Heathcliff"]

toons.each {|t| t = Cat.new(t)}

In irb, the last input and output are:

irb(main):008:0> toons.each {|t| t=Cat.new(t)}
=> ["Felix", "Garfield", "Heathcliff"]

which I don't understand.

Your code does create three instances of Cat, but they're thrown away
immediately, since you don't use them. Array#each always return the receiver
(in your case, the array ["Felix", "Garfield", "Heathcliff"]), regardless of
the return value of the block. If you want to obtain an array with the three
instances of Cat, use Array#map instead:

cats = toons.map{|n| Cat.new(name)}

Make that Cat.new(n) :slight_smile:

David

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4

Of course

Stefano

···

On Wednesday 30 April 2008, David A. Black wrote:

> cats = toons.map{|n| Cat.new(name)}

Make that Cat.new(n) :slight_smile:

5

David A. Black wrote:

Make that Cat.new(n) :slight_smile:

Hm. Shouldn't that be Cat.mew(n)? :stuck_out_tongue:

SCNR.

- --
Phillip Gawlowski
Twitter: twitter.com/cynicalryan
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