How do you write an equality method?

[David Corbin]

Without getting into the details of which equality method (eql?, equal?, ==),
I'm curious about how such a method should be written for class where you're
trying to keep the interface appropriatley private.

Consider:

class Foo
def initialize(color)
@color = color
end
.
.
.
end

If I do not wish to expose color via an attr_reader, how do I write an
equality method for this class?

David

[James Edward Gray II]

Use a protected accessor:

class Foo
def initialize( color )
@color = color
end

attr_reader :color
protected :color

def ==( other )
@color == other.color
end
end

Or cheat:

class Foo
def initialize( color )
@color = color
end

def ==( other )
@color == other.instance_eval { @color }
end
end

Hope that helps.

James Edward Gray II

[James Britt]

What would make two objects 'equal' ?

James
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[Dave Howell]

If Foo-class objects are the same if they have the same color . . .

redOne = Foo.new(red)
greenOne = Foo.new(green)
pineOne = Foo.new(green)

class Foo
def ==(other)
self.color == other.color
end
end

Now, redOne == greenOne is false. greenOne == pineOne is true.

I did something similar when trying to sort iTunes music tracks:

def <=>(other)
answer = self.artist <=> other.artist
answer = self.album <=> other.album if answer == 0
answer = self.name <=> other.name if answer == 0
answer = self.dbid <=> other.dbid if answer == 0
return answer
end