Hash#merge and setting defaults
18 Mar 2022When writing a method with an options Hash, how best do you specify default key/value pairs that can be safely overwritten?
Well, if it’s just one this should be fine:
def foo(k: 1)
p k
end
foo({ k: 'apple'})
but if you’re dealing with a double spat, Hash#merge is your friend.
# Can also use a constant here to help document what the defaults are
DEFAULTS = {
fruit: 'apple',
color: 'lavendar',
feels: 'sleepy'
}
def blog(**options)
options = DEFAULT.merge(options)
# ...
end
merge works like this:
h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.merge(h2) #=> {"a"=>100, "b"=>254, "c"=>300}
h1 #=> {"a"=>100, "b"=>200}
prioritizing the values in the Hash argument.
There’s also apparently Hash#reverse_merge in Rails, which handles duplicate values the other way— prioritizing the entries in the Hash calling the method.
h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.reverse_merge(h2) # => {"b"=>200, "c"=>300, "a"=>100}