# a is the array we want to turn into a hash
Hash[*a.zip([true] * a.size).flatten]

# Example:
people= %w[John Mary Paul]
query_people=Hash[*people.zip([true] * people.size).flatten]

query_people["John"] # returns true
query_people["Wenceslas"] # returns nil (equivalent to false in most tests)

Useful for speeding up searches.

Turning array values into hash keys

array

Ruby