Nithin Bekal 11 Jul 2025
Stop memoizing Hash lookups in Ruby
When a method performs a slow operation, memoizing the result using instance variables is a useful optimization. However, I’ve often seen people (including myself, sometimes!) reaching for memoization for things that don’t need to be optimized.
One common example is when there’s a class that wraps a Hash object. Hashes in Ruby are quite well optimized, so do you really need to memoize the result of the hash lookup? Let’s benchmark and find out.
Benchmarks
Let’s start with a simple Setting class that takes a data hash with type and value keys.
class Setting
def initialize(data)
@data = data
end
def type
@data["type"]
end
def type_memoized
@type ||= @data["type"]
…There’s a type method here, and I’ve added a type_memoized method for comparison.
Now let’s…
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