I have a simple array: arr = ["apples", "bananas", "coconuts", "watermelons"] I also have a function f that will perform an operation on a single string input and return a value. This operation is very expensive, so I would like to memoize the results in the hash. I know I can make the desired hash with something like this: h = {} arr.each { |a| h[a] = f(a) } What I'd like to do is not have to initialize h, so that I can just write something like this: h = arr.(???) { |a| a => f(a) } Can that be done?