How to make object instance a hash key in Ruby?
hashmap, ruby
Solution
See `Hash`:
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.
Problem
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