How to make object instance a hash key in Ruby?
See http://ruby-doc.org/core/classes/Hash.html
Hash uses key.eql? to test keys for equality. If you need to use instances of your own classes as keys in a Hash, it is recommended that you define both the eql? and hash methods. The hash method must have the property that a.eql?(b) implies a.hash == b.hash.
The eql? method is easy to implement: return true if all member variables are the same. For the hash method, use [@data1, @data2].hash as Marc-Andre suggests in the comments.
![Poul](https://i.stack.imgur.com/ALdyX.png?s=256&g=1)
Comments
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Poul about 2 years
I have a class Foo with a few member variables. When all values in two instances of the class are equal I want the objects to be 'equal'. I'd then like these objects to be keys in my hash. When I currently try this, the hash treats each instance as unequal.
h = {} f1 = Foo.new(a,b) f2 = Foo.new(a,b)
f1 and f2 should be equal at this point.
h[f1] = 7 h[f2] = 8 puts h[f1]
should print 8