class Hash(K, V)

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

Defined in:

hash.cr
json/any.cr
json/to_json.cr
yaml/any.cr
yaml/to_yaml.cr

Constructors

Class Method Summary

Instance Method Summary

Instance methods inherited from module Iterable({K, V})

chunk(reuse = false, &block : {K, V} -> U) forall U chunk, chunk_while(reuse : Bool | Array({K, V}) = false, &block : {K, V}, {K, V} -> B) forall B chunk_while, cycle(n)
cycle
cycle
, each each, each_cons(count : Int, reuse = false) each_cons, each_slice(count : Int, reuse = false) each_slice, each_with_index(offset = 0) each_with_index, each_with_object(obj) each_with_object, slice_after(reuse : Bool | Array({K, V}) = false, &block : {K, V} -> B) forall B
slice_after(pattern, reuse : Bool | Array({K, V}) = false)
slice_after
, slice_before(reuse : Bool | Array({K, V}) = false, &block : {K, V} -> B) forall B
slice_before(pattern, reuse : Bool | Array({K, V}) = false)
slice_before
, slice_when(reuse : Bool | Array({K, V}) = false, &block : {K, V}, {K, V} -> B) forall B slice_when

Instance methods inherited from module Enumerable({K, V})

all?(&)
all?(pattern)
all?
all?
, any?(&)
any?(pattern)
any?
any?
, chunks(&block : {K, V} -> U) forall U chunks, compact_map(&) compact_map, count(&)
count(item)
count
, cycle(n, &)
cycle(&)
cycle
, each(&block : {K, V} -> _) each, each_cons(count : Int, reuse = false, &) each_cons, each_cons_pair(& : {K, V}, {K, V} -> _) : Nil each_cons_pair, each_slice(count : Int, reuse = false, &) each_slice, each_with_index(offset = 0, &) each_with_index, each_with_object(obj, &) each_with_object, find(if_none = nil, &) find, first(count : Int)
first
first
, first? first?, flat_map(&block : {K, V} -> Array(U) | Iterator(U) | U) forall U flat_map, grep(pattern) grep, group_by(&block : {K, V} -> U) forall U group_by, in_groups_of(size : Int, filled_up_with : U = nil) forall U
in_groups_of(size : Int, filled_up_with : U = nil, reuse = false, &) forall U
in_groups_of
, includes?(obj) includes?, index(&)
index(obj)
index
, index_by(&block : {K, V} -> U) forall U index_by, join(separator = "", &)
join(separator, io, &)
join(separator, io)
join(separator = "")
join
, map(&block : {K, V} -> U) forall U map, map_with_index(offset = 0, &block : {K, V}, Int32 -> U) forall U map_with_index, max max, max? max?, max_by(&block : {K, V} -> U) forall U max_by, max_by?(&block : {K, V} -> U) forall U max_by?, max_of(&block : {K, V} -> U) forall U max_of, max_of?(&block : {K, V} -> U) forall U max_of?, min min, min? min?, min_by(&block : {K, V} -> U) forall U min_by, min_by?(&block : {K, V} -> U) forall U min_by?, min_of(&block : {K, V} -> U) forall U min_of, min_of?(&block : {K, V} -> U) forall U min_of?, minmax minmax, minmax? minmax?, minmax_by(&block : {K, V} -> U) forall U minmax_by, minmax_by?(&block : {K, V} -> U) forall U minmax_by?, minmax_of(&block : {K, V} -> U) forall U minmax_of, minmax_of?(&block : {K, V} -> U) forall U minmax_of?, none?
none?(pattern)
none?(&)
none?
, one?(&)
one?(pattern)
one?
one?
, partition(&) partition, product(&)
product(initial : Number, &)
product
product(initial : Number)
product
, reduce(memo, &)
reduce(&)
reduce
, reduce?(&) reduce?, reject(&block : {K, V} -> )
reject(type : U.class) forall U
reject(pattern)
reject
, select(pattern)
select(type : U.class) forall U
select(&block : {K, V} -> )
select
, size size, skip(count : Int) skip, skip_while(&) skip_while, sum(initial)
sum
sum(initial, &)
sum(&)
sum
, take_while(&) take_while, tally : Hash({K, V}, Int32) tally, to_a to_a, to_h
to_h(&block : {K, V} -> Tuple(K, V)) forall K, V
to_h
, to_set to_set, zip(*others : Indexable | Iterable | Iterator, &)
zip(*others : Indexable | Iterable | Iterator)
zip
, zip?(*others : Indexable | Iterable | Iterator, &)
zip?(*others : Indexable | Iterable | Iterator)
zip?

Instance methods inherited from class Reference

==(other : self)
==(other : JSON::Any)
==(other : YAML::Any)
==(other)
==
, dup dup, hash(hasher) hash, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference)
same?(other : Nil)
same?
, to_s(io : IO) : Nil to_s

Constructor methods inherited from class Reference

new new

Instance methods inherited from class Object

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other)
===
, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash
hash(hasher)
hash
, inspect(io : IO) : Nil
inspect : String
inspect
, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO)
to_json
to_json
, to_pretty_json(indent : String = " ")
to_pretty_json(io : IO, indent : String = " ")
to_pretty_json
, to_s : String
to_s(io : IO) : Nil
to_s
, to_yaml(io : IO)
to_yaml
to_yaml
, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

Constructor methods inherited from class Object

from_json(string_or_io, root : String) : self
from_json(string_or_io) : self
from_json
, from_yaml(string_or_io : String | IO) : self from_yaml

Constructor Detail

def self.new(default_value : V, initial_capacity = nil) #

Creates a new empty Hash where the default_value is returned if a key is missing.

inventory = Hash(String, Int32).new(0)
inventory["socks"] = 3
inventory["pickles"] # => 0

NOTE The default value is passed by reference:

arr = [1, 2, 3]
hash = Hash(String, Array(Int32)).new(arr)
hash["3"][1] = 4
arr # => [1, 4, 3]

The initial_capacity is useful to avoid unnecessary reallocations of the internal buffer in case of growth. If the number of elements a hash will hold is known, the hash should be initialized with that capacity for improved performance. Otherwise, the default is 11 and inputs less than 11 are ignored.


[View source]
def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node) #

[View source]
def self.new(pull : JSON::PullParser) #

Reads a Hash from the given pull parser.

Keys are read by invoking from_json_object_key? on this hash's key type (K), which must return a value of type K or nil. If nil is returned a JSON::ParseException is raised.

Values are parsed using the regular .new(pull : JSON::PullParser) method.


[View source]
def self.new #

Creates a new empty Hash.


[View source]
def self.new(block : Hash(K, V), K -> V? = nil, *, initial_capacity = nil) #

Creates a new empty Hash with a block for handling missing keys.

proc = ->(hash : Hash(String, Int32), key : String) { hash[key] = key.size }
hash = Hash(String, Int32).new(proc)

hash.size   # => 0
hash["foo"] # => 3
hash.size   # => 1
hash["bar"] = 10
hash["bar"] # => 10

The initial_capacity is useful to avoid unnecessary reallocations of the internal buffer in case of growth. If the number of elements a hash will hold is known, the hash should be initialized with that capacity for improved performance. Otherwise, the default is 11 and inputs less than 11 are ignored.


[View source]
def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node, &) #

[View source]
def self.new(initial_capacity = nil, &block : Hash(K, V), K -> V) #

Creates a new empty Hash with a block that handles missing keys.

hash = Hash(String, Int32).new do |hash, key|
  hash[key] = key.size
end

hash.size   # => 0
hash["foo"] # => 3
hash.size   # => 1
hash["bar"] = 10
hash["bar"] # => 10

The initial_capacity is useful to avoid unnecessary reallocations of the internal buffer in case of growth. If the number of elements a hash will hold is known, the hash should be initialized with that capacity for improved performance. Otherwise, the default is 11 and inputs less than 11 are ignored.


[View source]

Class Method Detail

def self.zip(ary1 : Array(K), ary2 : Array(V)) #

Zips two arrays into a Hash, taking keys from ary1 and values from ary2.

Hash.zip(["key1", "key2", "key3"], ["value1", "value2", "value3"])
# => {"key1" => "value1", "key2" => "value2", "key3" => "value3"}

[View source]

Instance Method Detail

def ==(other : YAML::Any) #

[View source]
def ==(other : JSON::Any) #

[View source]
def ==(other : Hash) #

Compares with other. Returns true if all key-value pairs are the same.


[View source]
def [](key) #

Returns the value for the key given by key. If not found, returns the default value given by Hash.new, otherwise raises KeyError.

h = {"foo" => "bar"}
h["foo"] # => "bar"

h = Hash(String, String).new("bar")
h["foo"] # => "bar"

h = Hash(String, String).new { "bar" }
h["foo"] # => "bar"

h = Hash(String, String).new
h["foo"] # raises KeyError

[View source]
def []=(key : K, value : V) #

Sets the value of key to the given value.

h = {} of String => String
h["foo"] = "bar"
h["foo"] # => "bar"

[View source]
def []?(key) #

Returns the value for the key given by key. If not found, returns nil. This ignores the default value set by Hash.new.

h = {"foo" => "bar"}
h["foo"]? # => "bar"
h["bar"]? # => nil

h = Hash(String, String).new("bar")
h["foo"]? # => nil

[View source]
def clear #

Empties a Hash and returns it.

hash = {"foo" => "bar"}
hash.clear # => {}

[View source]
def clone #

Similar to #dup, but duplicates the values as well.

hash_a = {"foobar" => {"foo" => "bar"}}
hash_b = hash_a.clone
hash_b["foobar"]["foo"] = "baz"
hash_a # => {"foobar" => {"foo" => "bar"}}

[View source]
def compact #

Returns new Hash without nil values.

hash = {"hello" => "world", "foo" => nil}
hash.compact # => {"hello" => "world"}

[View source]
def compact! #

Removes all nil value from self. Returns nil if no changes were made.

hash = {"hello" => "world", "foo" => nil}
hash.compact! # => {"hello" => "world"}
hash.compact! # => nil

[View source]
def compare_by_identity #

Makes this hash compare keys using their object identity (object_id) for types that define such method (Reference types, but also structs that might wrap other Reference types and delegate the object_id method to them).

h1 = {"foo" => 1, "bar" => 2}
h1["fo" + "o"]? # => 1

h1.compare_by_identity
h1.compare_by_identity? # => true
h1["fo" + "o"]?         # => nil # not the same String instance

[View source]
def compare_by_identity? #

Returns true of this Hash is comparing keys by object_id.

See #compare_by_identity.


[View source]
def delete(key, &) #

Deletes the key-value pair and returns the value, else yields key with given block.

h = {"foo" => "bar"}
h.delete("foo") { |key| "#{key} not found" } # => "bar"
h.fetch("foo", nil)                          # => nil
h.delete("baz") { |key| "#{key} not found" } # => "baz not found"

[View source]
def delete(key) #

Deletes the key-value pair and returns the value, otherwise returns nil.

h = {"foo" => "bar"}
h.delete("foo")     # => "bar"
h.fetch("foo", nil) # => nil

[View source]
def delete_if(&) #

Deletes each key-value pair for which the given block returns true.

h = {"foo" => "bar", "fob" => "baz", "bar" => "qux"}
h.delete_if { |key, value| key.starts_with?("fo") }
h # => { "bar" => "qux" }

[View source]
def dig(key : K, *subkeys) #

Traverses the depth of a structure and returns the value, otherwise raises KeyError.

h = {"a" => {"b" => [10, 20, 30]}}
h.dig "a", "b"                # => [10, 20, 30]
h.dig "a", "b", "c", "d", "e" # raises KeyError

[View source]
def dig?(key : K, *subkeys) #

Traverses the depth of a structure and returns the value. Returns nil if not found.

h = {"a" => {"b" => [10, 20, 30]}}
h.dig? "a", "b"                # => [10, 20, 30]
h.dig? "a", "b", "c", "d", "e" # => nil

[View source]
def dup #

Duplicates a Hash.

hash_a = {"foo" => "bar"}
hash_b = hash_a.dup
hash_b.merge!({"baz" => "qux"})
hash_a # => {"foo" => "bar"}

[View source]
def each #

Returns an iterator over the hash entries. Which behaves like an Iterator returning a Tuple consisting of the key and value types.

hsh = {"foo" => "bar", "baz" => "qux"}
iterator = hsh.each

iterator.next # => {"foo", "bar"}
iterator.next # => {"baz", "qux"}

The enumeration follows the order the keys were inserted.


[View source]
def each(&) : Nil #

Calls the given block for each key-value pair and passes in the key and the value.

h = {"foo" => "bar"}

h.each do |key, value|
  key   # => "foo"
  value # => "bar"
end

h.each do |key_and_value|
  key_and_value # => {"foo", "bar"}
end

The enumeration follows the order the keys were inserted.


[View source]
def each_key(&) #

Calls the given block for each key-value pair and passes in the key.

h = {"foo" => "bar"}
h.each_key do |key|
  key # => "foo"
end

The enumeration follows the order the keys were inserted.


[View source]
def each_key #

Returns an iterator over the hash keys. Which behaves like an Iterator consisting of the key's types.

hsh = {"foo" => "bar", "baz" => "qux"}
iterator = hsh.each_key

key = iterator.next
key # => "foo"

key = iterator.next
key # => "baz"

The enumeration follows the order the keys were inserted.


[View source]
def each_value(&) #

Calls the given block for each key-value pair and passes in the value.

h = {"foo" => "bar"}
h.each_value do |value|
  value # => "bar"
end

The enumeration follows the order the keys were inserted.


[View source]
def each_value #

Returns an iterator over the hash values. Which behaves like an Iterator consisting of the value's types.

hsh = {"foo" => "bar", "baz" => "qux"}
iterator = hsh.each_value

value = iterator.next
value # => "bar"

value = iterator.next
value # => "qux"

The enumeration follows the order the keys were inserted.


[View source]
def empty? #

Returns true when hash contains no key-value pairs.

h = Hash(String, String).new
h.empty? # => true

h = {"foo" => "bar"}
h.empty? # => false

[View source]
def fetch(key, default) #

Returns the value for the key given by key, or when not found the value given by default. This ignores the default value set by Hash.new.

h = {"foo" => "bar"}
h.fetch("foo", "foo") # => "bar"
h.fetch("bar", "foo") # => "foo"

[View source]
def fetch(key, &) #

Returns the value for the key given by key, or when not found calls the given block with the key.

h = {"foo" => "bar"}
h.fetch("foo") { "default value" }  # => "bar"
h.fetch("bar") { "default value" }  # => "default value"
h.fetch("bar") { |key| key.upcase } # => "BAR"

[View source]
def first_key #

Returns the first key in the hash.


[View source]
def first_key? #

Returns the first key if it exists, or returns nil.

hash = {"foo1" => "bar1", "foz2" => "baz2"}
hash.first_key? # => "foo1"
hash.clear
hash.first_key? # => nil

[View source]
def first_value #

Returns the first value in the hash.


[View source]
def first_value? #

Returns the first value if it exists, or returns nil.

hash = {"foo1" => "bar1", "foz2" => "baz2"}
hash.first_value? # => "bar1"
hash.clear
hash.first_value? # => nil

[View source]
def has_key?(key) #

Returns true when key given by key exists, otherwise false.

h = {"foo" => "bar"}
h.has_key?("foo") # => true
h.has_key?("bar") # => false

[View source]
def has_value?(val) #

Returns true when value given by value exists, otherwise false.

h = {"foo" => "bar"}
h.has_value?("foo") # => false
h.has_value?("bar") # => true

[View source]
def hash(hasher) #

[View source]
def inspect(io : IO) : Nil #
Description copied from class Reference

Appends a String representation of this object which includes its class name, its object address and the values of all instance variables.

class Person
  def initialize(@name : String, @age : Int32)
  end
end

Person.new("John", 32).inspect # => #<Person:0x10fd31f20 @name="John", @age=32>

[View source]
def invert #

Inverts keys and values. If there are duplicated values, the last key becomes the new value.

{"foo" => "bar"}.invert                 # => {"bar" => "foo"}
{"foo" => "bar", "baz" => "bar"}.invert # => {"bar" => "baz"}

[View source]
def key_for(value) #

Returns a key with the given value, else raises KeyError.

hash = {"foo" => "bar", "baz" => "qux"}
hash.key_for("bar")    # => "foo"
hash.key_for("qux")    # => "baz"
hash.key_for("foobar") # raises KeyError (Missing hash key for value: foobar)

[View source]
def key_for(value, &) #

Returns a key with the given value, else yields value with the given block.

hash = {"foo" => "bar"}
hash.key_for("bar") { |value| value.upcase } # => "foo"
hash.key_for("qux") { |value| value.upcase } # => "QUX"

[View source]
def key_for?(value) #

Returns a key with the given value, else nil.

hash = {"foo" => "bar", "baz" => "qux"}
hash.key_for?("bar")    # => "foo"
hash.key_for?("qux")    # => "baz"
hash.key_for?("foobar") # => nil

[View source]
def key_index(key) #

Returns the index of the given key, or nil when not found. The keys are ordered based on when they were inserted.

h = {"foo" => "bar", "baz" => "qux"}
h.key_index("foo") # => 0
h.key_index("qux") # => nil

[View source]
def keys : Array(K) #

Returns a new Array with all the keys.

h = {"foo" => "bar", "baz" => "bar"}
h.keys # => ["foo", "baz"]

[View source]
def last_key #

Returns the last key in the hash.


[View source]
def last_key? #

Returns the last key if it exists, or returns nil.

hash = {"foo1" => "bar1", "foz2" => "baz2"}
hash.last_key? # => "foz2"
hash.clear
hash.last_key? # => nil

[View source]
def last_value #

Returns the last value in the hash.


[View source]
def last_value? #

Returns the last value if it exists, or returns nil.

hash = {"foo1" => "bar1", "foz2" => "baz2"}
hash.last_value? # => "baz2"
hash.clear
hash.last_value? # => nil

[View source]
def merge(other : Hash(L, W), &block : K, V, W -> V | W) forall L, W #

[View source]
def merge(other : Hash(L, W)) forall L, W #

Returns a new Hash with the keys and values of this hash and other combined. A value in other takes precedence over the one in this hash.

hash = {"foo" => "bar"}
hash.merge({"baz" => "qux"})
# => {"foo" => "bar", "baz" => "qux"}
hash
# => {"foo" => "bar"}

[View source]
def merge!(other : Hash) #

Similar to #merge, but the receiver is modified.

hash = {"foo" => "bar"}
hash.merge!({"baz" => "qux"})
hash # => {"foo" => "bar", "baz" => "qux"}

[View source]
def merge!(other : Hash, &) : self #

Adds the contents of other to this hash. If a key exists in both hashes, the given block is called to determine the value to be used. The block arguments are the key, the value in self and the value in other.

hash = {"a" => 100, "b" => 200}
other = {"b" => 254, "c" => 300}
hash.merge!(other) { |key, v1, v2| v1 + v2 }
hash # => {"a" => 100, "b" => 454, "c" => 300}

[View source]
def pretty_print(pp) : Nil #

[View source]
def put(key : K, value : V, &) #

Sets the value of key to the given value.

If a value already exists for key, that (old) value is returned. Otherwise the given block is invoked with key and its value is returned.

h = {} of Int32 => String
h.put(1, "one") { "didn't exist" } # => "didn't exist"
h.put(1, "uno") { "didn't exist" } # => "one"
h.put(2, "two") { |key| key.to_s } # => "2"

[View source]
def rehash : Nil #

Rebuilds the hash table based on the current value of each key.

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 method re-indexes the hash using the current key values.


[View source]
def reject(*keys) #

Returns a new Hash without the given keys.

{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.reject("a", "c") # => {"b" => 2, "d" => 4}

[View source]
def reject(&block : K, V -> _) #

Returns a new hash consisting of entries for which the block returns false.

h = {"a" => 100, "b" => 200, "c" => 300}
h.reject { |k, v| k > "a" } # => {"a" => 100}
h.reject { |k, v| v < 200 } # => {"b" => 200, "c" => 300}

[View source]
def reject!(*keys) #

[View source]
def reject!(keys : Array | Tuple) #

Removes a list of keys out of hash.

h = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.reject!("a", "c")
h # => {"b" => 2, "d" => 4}

[View source]
def reject!(&block : K, V -> _) #

Equivalent to Hash#reject, but makes modification on the current object rather that returning a new one. Returns nil if no changes were made.


[View source]
def select(&block : K, V -> _) #

Returns a new hash consisting of entries for which the block returns true.

h = {"a" => 100, "b" => 200, "c" => 300}
h.select { |k, v| k > "a" } # => {"b" => 200, "c" => 300}
h.select { |k, v| v < 200 } # => {"a" => 100}

[View source]
def select(keys : Array | Tuple) #

Returns a new Hash with the given keys.

{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select({"a", "c"}) # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select("a", "c")   # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select(["a", "c"]) # => {"a" => 1, "c" => 3}

[View source]
def select(*keys) #

Returns a new Hash with the given keys.

{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select({"a", "c"}) # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select("a", "c")   # => {"a" => 1, "c" => 3}
{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select(["a", "c"]) # => {"a" => 1, "c" => 3}

[View source]
def select!(&block : K, V -> _) #

Equivalent to Hash#select but makes modification on the current object rather that returning a new one. Returns nil if no changes were made


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def select!(*keys) #

Removes every element except the given ones.

h1 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!({"a", "c"})
h2 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!("a", "c")
h3 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!(["a", "c"])
h1 == h2 == h3 # => true
h1             # => {"a" => 1, "c" => 3}

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def select!(keys : Array | Tuple) #

Removes every element except the given ones.

h1 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!({"a", "c"})
h2 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!("a", "c")
h3 = {"a" => 1, "b" => 2, "c" => 3, "d" => 4}.select!(["a", "c"])
h1 == h2 == h3 # => true
h1             # => {"a" => 1, "c" => 3}

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def shift #

Deletes and returns the first key-value pair in the hash, or raises IndexError if the hash is empty.

hash = {"foo" => "bar", "baz" => "qux"}
hash.shift # => {"foo", "bar"}
hash       # => {"baz" => "qux"}

hash = {} of String => String
hash.shift # raises IndexError

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def shift(&) #

Deletes and returns the first key-value pair in the hash. Yields to the given block if the hash is empty.

hash = {"foo" => "bar", "baz" => "qux"}
hash.shift { true } # => {"foo", "bar"}
hash                # => {"baz" => "qux"}

hash = {} of String => String
hash.shift { true } # => true
hash                # => {}

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def shift? #

Same as #shift, but returns nil if the hash is empty.

hash = {"foo" => "bar", "baz" => "qux"}
hash.shift? # => {"foo", "bar"}
hash        # => {"baz" => "qux"}

hash = {} of String => String
hash.shift? # => nil

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def size : Int32 #

Returns the number of elements in this Hash.


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def to_a : Array(Tuple(K, V)) #

Returns an array of tuples with key and values belonging to this Hash.

h = {1 => 'a', 2 => 'b', 3 => 'c'}
h.to_a # => [{1, 'a'}, {2, 'b'}, {3, 'c'}]

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def to_h #

Returns self.


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def to_json(json : JSON::Builder) #

Serializes this Hash into JSON.

Keys are serialized by invoking to_json_object_key on them. Values are serialized with the usual #to_json(json : JSON::Builder) method.


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def to_s(io : IO) : Nil #

Converts to a String.

h = {"foo" => "bar"}
h.to_s       # => "{\"foo\" => \"bar\"}"
h.to_s.class # => String

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def to_yaml(yaml : YAML::Nodes::Builder) #

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def transform_keys(&block : K -> K2) forall K2 #

Returns a new hash with all keys converted using the block operation. The block can change a type of keys.

hash = {:a => 1, :b => 2, :c => 3}
hash.transform_keys { |key| key.to_s } # => {"a" => 1, "b" => 2, "c" => 3}

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def transform_values(&block : V -> V2) forall V2 #

Returns a new hash with the results of running block once for every value. The block can change a type of values.

hash = {:a => 1, :b => 2, :c => 3}
hash.transform_values { |value| value + 1 } # => {:a => 2, :b => 3, :c => 4}

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def transform_values!(&block : V -> V) #

Destructively transforms all values using a block. Same as transform_values but modifies in place. The block cannot change a type of values.

hash = {:a => 1, :b => 2, :c => 3}
hash.transform_values! { |value| value + 1 }
hash # => {:a => 2, :b => 3, :c => 4}

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def values : Array(V) #

Returns only the values as an Array.

h = {"foo" => "bar", "baz" => "qux"}
h.values # => ["bar", "qux"]

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def values_at(*indexes : K) #

Returns a tuple populated with the elements at the given indexes. Raises if any index is invalid.

{"a" => 1, "b" => 2, "c" => 3, "d" => 4}.values_at("a", "c") # => {1, 3}

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