Hash.fetch / store / delete / merge

hash.fetch(key)
hash.fetch(key, default)
hash.fetch(key) { |k| compute default }

# Sets a key-value pair.
hash.store(key, value)
hash[key] = value

# Removes a key and its associated value.
hash.delete(key)
hash.delete(key) { |k| value to return if not found }

# Returns a new hash that merges two hashes together.
hash.merge(other_hash)
hash.merge(other_hash) { |key, old, new| handle conflict }
hash.merge!(other_hash) # destructive

sample_hash_fetch_store_delete_merge.rb

config = { host: 'localhost', port: 3000 }

# fetch: safely access potentially missing keys
puts config.fetch(:host) # "localhost"
puts config.fetch(:timeout, 30) # 30 (default value)
puts config.fetch(:name) { |k| "#{k} is not configured" }
# => "name is not configured"

# store / []= to set values
config.store(:ssl, false)
config[:debug] = true
puts config.inspect
# {host: "localhost", port: 3000, ssl: false, debug: true}

# delete to remove a key
deleted = config.delete(:debug)
puts deleted # true (the deleted value)
puts config.inspect # {host: "localhost", port: 3000, ssl: false}

# merge: combine hashes
defaults = { timeout: 60, retry: 3, debug: false }
custom = { debug: true, host: 'example.com' }
merged = defaults.merge(custom)
puts merged.inspect
# {timeout: 60, retry: 3, debug: true, host: "example.com"}

# merge with a block to handle key conflicts
h1 = { a: 1, b: 2 }
h2 = { b: 3, c: 4 }
result = h1.merge(h2) { |key, old, new_val| old + new_val }
puts result.inspect # {a: 1, b: 5, c: 4} (b is 2+3=5, not 1+2+3)

# slice: extract only the keys you need
user = { id: 1, name: 'Ryomen Sukuna', password: 'secret', email: 'ryomen_sukuna@wp-p.info' }
public_info = user.slice(:id, :name, :email)
puts public_info.inspect # {id: 1, name: "Ryomen Sukuna", email: "ryomen_sukuna@wp-p.info"}

hash_fetch_store_delete_merge.rb

ruby hash_fetch_store_delete_merge.rb
localhost
30
name is not configured
{host: "localhost", port: 3000, ssl: false, debug: true}
true
{host: "localhost", port: 3000, ssl: false}
{timeout: 60, retry: 3, debug: true, host: "example.com"}
{a: 1, b: 5, c: 4}
{id: 1, name: "Ryomen Sukuna", email: "ryomen_sukuna@wp-p.info"}

Accessing a key with [] silently returns nil if the key does not exist. To prevent unexpected nil values from creeping in, use fetch when a key is required. Since fetch raises a KeyError when a key is missing, it helps you catch bugs early.

merge is a non-destructive method that returns a new hash. If you want to modify the original hash in place, use merge! (or its alias update). You can pass a block to fine-tune how conflicting keys are resolved.

slice, added in Ruby 2.5, is useful for extracting only the keys you need from a hash — for example, to strip unwanted fields from an API response. To exclude specific keys instead, use reject.