class Hash(K, V)

• Hash(K, V)
• Reference
• Object

Overview

A Hash represents a collection of key-value mappings, similar to a dictionary.

Main operations are storing a key-value mapping (#[]=) and querying the value associated to a key (#[]). Key-value mappings can also be deleted (#delete). Keys are unique within a hash. When adding a key-value mapping with a key that is already in use, the old value will be forgotten.

# Create a new Hash for mapping String to Int32
hash = Hash(String, Int32).new
hash["one"] = 1
hash["two"] = 2
hash["one"] # => 1

Hash literals can also be used to create a Hash:

{"one" => 1, "two" => 2}

Implementation is based on an open hash table. Two objects refer to the same hash key when their hash value (Object#hash) is identical and both objects are equal to each other (Object#==).

Enumeration follows the order that the corresponding keys were inserted.

NOTE When using mutable data types as keys, changing the value of a key after it was inserted into the Hash may lead to undefined behaviour. This can be restored by re-indexing the hash with #rehash.

Included Modules

• Enumerable({K, V})
• Iterable({K, V})

Defined in:

Instance Method Summary

• #compact

  Returns a hash with non nil values.

• #compact!

  Replaces current hash with non nil values.

• #to_param

  Alias for to_query

• #to_query(namespace = nil)

  Returns a string representation of the receiver suitable for use as a URL query string:

Instance Method Detail

hash = { a: true, b: false, c: nil}
hash.compact # => { a: true, b: false }
hash # => { a: true, b: false, c: nil}
{ c: nil }.compact # => {}

hash = { a: true, b: false, c: nil }
hash.compact! # => { a: true, b: false }
hash # => { a: true, b: false }

{name: "David", nationality: "Danish"}.to_query
# => "name=David&nationality=Danish"

{name: "David", nationality: "Danish"}.to_query("user")
# => "user%5Bname%5D=David&user%5Bnationality%5D=Danish"