struct NamedTuple(**T)

Overview

A named tuple is a fixed-size, immutable, stack-allocated mapping of a fixed set of keys to values.

You can think of a NamedTuple as an immutable Hash whose keys (which are of type Symbol), and the types for each key, are known at compile time.

A named tuple can be created with a named tuple literal:

language = {name: "Crystal", year: 2011} # NamedTuple(name: String, year: Int32)

language[:name]  # => "Crystal" (String)
language[:year]  # => 2011      (Int32)
language[:other] # compile time error

The compiler knows what types are in each key, so when indexing a named tuple with a symbol literal the compiler will return the value for that key and with the expected type, like in the above snippet. Indexing with a symbol literal for which there's no key will give a compile-time error.

Indexing with a symbol that is only known at runtime will return a value whose type is the union of all the types in the named tuple, and might raise KeyError.

Defined in:

named_tuple.cr
json/to_json.cr
yaml/to_yaml.cr

Class Method Summary

Instance Method Summary

Instance methods inherited from struct Value

==(other) ==, dup dup

Instance methods inherited from class Object

!=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other)
===
, =~(other) =~, class class, crystal_type_id crystal_type_id, dup dup, hash hash, inspect(io : IO)
inspect
inspect
, itself itself, not_nil! not_nil!, tap(&block) tap, to_json to_json, to_pretty_json(indent : String = " ")
to_pretty_json(io : IO, indent : String = " ")
to_pretty_json
, to_s
to_s(io : IO)
to_s
, to_yaml(io : IO)
to_yaml
to_yaml
, try(&block) try

Class methods inherited from class Object

==(other : Class) ==, ===(other) ===, cast(other) : self cast, clone clone, dup dup, from_json(string_or_io, root : String) : self
from_json(string_or_io) : self
from_json
, from_yaml(string : String) : self from_yaml, hash hash, inspect(io) inspect, name : String name, nilable? nilable?, to_s(io) to_s, |(other : U.class) forall U |

Class Method Detail

def self.from(hash : Hash) #

Creates a named tuple from the given hash, with elements casted to the given types. See #from.

NamedTuple(foo: String, bar: Int64).from({:foo => "world", :bar => 2})       # => {foo: "world", bar: 2}
NamedTuple(foo: String, bar: Int64).from({"foo" => "world", "bar" => 2})     # => {foo: "world", bar: 2}
NamedTuple(foo: String, bar: Int64).from({:foo => "world", :bar => 2}).class # => {foo: String, bar: Int64}

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def self.new(pull : JSON::PullParser) #

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def self.new(pull : YAML::PullParser) #

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def self.new #

Creates a named tuple that will contain the given arguments.

This method is useful in macros and generic code because with it you can creates empty named tuples, something that you can't do with a tuple literal.

NamedTuple.new(name: "Crystal", year: 2011) #=> {name: "Crystal", year: 2011}
NamedTuple.new                  #=> {}

{}                         # syntax error

[View source]

Instance Method Detail

def ==(other : NamedTuple) #

Returns true if this tuple has the same keys as other, and values for each key are the same in self and other.

tuple1 = {name: "Crystal", year: 2011}
tuple2 = {year: 2011, name: "Crystal"}
tuple3 = {name: "Crystal", year: 2012}
tuple4 = {name: "Crystal", year: 2011.0}

tuple1 == tuple2 # => true
tuple1 == tuple3 # => false
tuple1 == tuple4 # => true

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def ==(other : self) #

Returns true if this tuple has the same keys as other, and values for each key are the same in self and other.

tuple1 = {name: "Crystal", year: 2011}
tuple2 = {year: 2011, name: "Crystal"}
tuple3 = {name: "Crystal", year: 2012}
tuple4 = {name: "Crystal", year: 2011.0}

tuple1 == tuple2 # => true
tuple1 == tuple3 # => false
tuple1 == tuple4 # => true

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def [](key : Symbol | String) #

Returns the value for the given key, if there's such key, otherwise raises KeyError.

tuple = {name: "Crystal", year: 2011}

key = :name
tuple[key] # => "Crystal"

key = "year"
tuple[key] # => 2011

key = :other
tuple[key] # # => KeyError

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def []?(key : Symbol | String) #

Returns the value for the given key, if there's such key, otherwise returns nil.

tuple = {name: "Crystal", year: 2011}

key = :name
tuple[key]? # => "Crystal"

key = "year"
tuple[key] # => 2011

key = :other
tuple[key]? # => nil

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def clone #

Returns a named tuple with the same keys but with cloned values, using the #clone method.


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def each(&block) #

Yields each key and value in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.each do |key, value|
  puts "#{key} = #{value}"
end

Output:

name = Crystal
year = 2011

[View source]
def each_key(&block) #

Yields each key in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.each_key do |key|
  puts key
end

Output:

name
year

[View source]
def each_value(&block) #

Yields each value in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.each_value do |value|
  puts value
end

Output:

Crystal
2011

[View source]
def each_with_index(offset = 0, &block) #

Yields each key and value, together with an index starting at offset, in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.each_with_index do |key, value, i|
  puts "#{i + 1}) #{key} = #{value}"
end

Output:

1) name = Crystal
2) year = 2011

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def empty? #

Returns true if this named tuple is empty.

tuple = {name: "Crystal", year: 2011}
tuple.empty? # => false

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def fetch(key : Symbol | String, default_value) #

Returns the value for the given key, if there's such key, otherwise returns default_value.

tuple = {name: "Crystal", year: 2011}
tuple.fetch(:name, "Unknown") # => "Crystal"
tuple.fetch("year", 0)        # => 2011
tuple.fetch(:other, 0)        # => 0

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def fetch(key : Symbol, &block) #

Returns the value for the given key, if there's such key, otherwise the value returned by the block.

tuple = {name: "Crystal", year: 2011}
tuple.fetch(:name) { "Unknown" } # => "Crystal"
tuple.fetch(:other) { 0 }        # => 0

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def fetch(key : String, &block) #

Returns the value for the given key, if there's such key, otherwise the value returned by the block.

tuple = {name: "Crystal", year: 2011}
tuple.fetch("name") { "Unknown" } # => "Crystal"
tuple.fetch("other") { 0 }        # => 0

[View source]
def from(hash : Hash) #

Expects to be called on a named tuple whose values are types, creates a tuple from the given hash, with types casted appropriately. The hash keys must be either symbols or strings.

This allows you to easily pass a hash as individual named arguments to a method.

def speak_about(thing : String, n : Int64)
  "I see #{n} #{thing}s"
end

data = JSON.parse(%({"thing": "world", "n": 2})).as_h
speak_about(**{thing: String, n: Int64}.from(data)) # => "I see 2 worlds"

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def has_key?(key : Symbol) : Bool #

Returns true if this named tuple has the given key, false otherwise.

tuple = {name: "Crystal", year: 2011}
tuple.has_key?(:name)  # => true
tuple.has_key?(:other) # => false

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def hash #

Returns a hash value based on this name tuple's size, keys and values.

See Object#hash.


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def inspect #

Same as #to_s.


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def keys #

Returns a Tuple of symbols with the keys in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.keys # => {:name, :year}

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def map(&block) #

Returns an Array populated with the results of each iteration in the given block, which is given each key and value in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.map { |k, v| "#{name}: #{year}" } # => ["name: Crystal", "year: 2011"]

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def size #

Returns the number of elements in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.size # => 2

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def to_a #

Returns a new Array of tuples populated with each key-value pair.

tuple = {name: "Crystal", year: 2011}
tuple.to_a # => [{:name, "Crystal"}, {:year, 2011}]

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def to_h #

Returns a Hash with the keys and values in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.to_h # => {:name => "Crystal", :year => 2011}

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def to_json(io : IO) #

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def to_s(io) #

Appends a string representation of this named tuple to the given IO.

tuple = {name: "Crystal", year: 2011}
tuple.to_s # => %({name: "Crystal", year: 2011})

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def to_yaml(emitter : YAML::Emitter) #

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def values #

Returns a Tuple with the values in this named tuple.

tuple = {name: "Crystal", year: 2011}
tuple.values # => {"Crystal", 2011}

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