struct NamedTuple(**T)
inherits Value

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"
language[:year]  # => 2011
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.

Class methods

.types

Returns the types of this named tuple type.

tuple = {a: 1, b: "hello", c: 'x'}
tuple.class.types # => {a: Int32, b: String, c: Char}

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.from(hash : Hash) : self

Creates a named tuple from the given hash, with elements casted to the given types. Here the Int32 | String union is cast to Int32.

num_or_str = 42.as(Int32 | String)
NamedTuple(name: String, val: Int32).from({"name" => "number", "val" => num_or_str}) # => {name: "number", val: 42}

num_or_str = "a string".as(Int32 | String)
NamedTuple(name: String, val: Int32).from({"name" => "number", "val" => num_or_str}) # raises TypeCastError (cast from String to Int32 failed)

See also: #from.

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.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node)

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.new(pull : JSON::PullParser)

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.new(**options : **T)

Creates a named tuple that will contain the given arguments.

With a named tuple literal you cannot create an empty named tuple. This method doesn't have this limitation, which makes it especially useful in macros and generic code.

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

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Methods

#==(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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#==(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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#[](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] # raises KeyError

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#[]?(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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#clone

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

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#dig(key : Symbol | String, *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

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#dig?(key : Symbol | String, *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

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#each(&) : Nil

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

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#each_key(&) : Nil

Yields each key in this named tuple.

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

Output:

name
year

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#each_value(&) : Nil

Yields each value in this named tuple.

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

Output:

Crystal
2011

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#each_with_index(offset = 0

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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#empty?

Returns true if this named tuple is empty.

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

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#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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#fetch(key : Symbol

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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#fetch(key : String

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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#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.

require "json"

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

hash = JSON.parse(%({"thing": "world", "n": 2})).as_h # hash : Hash(String, JSON::Any)
hash = hash.transform_values(&.raw)                   # hash : Hash(String, JSON::Any::Type)

speak_about(**{thing: String, n: Int64}.from(hash)) # => "I see 2 worlds"

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#has_key?(key : String) : 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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#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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#hash(hasher)

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

See also: Object#hash. See Object#hash(hasher)

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#inspect : String

Same as to_s.

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#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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#map

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

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#merge(other : NamedTuple)

Merges two named tuples into one, returning a new named tuple. If a key is defined in both tuples, the value and its type is used from other.

a = {foo: "Hello", bar: "Old"}
b = {bar: "New", baz: "Bye"}
a.merge(b) # => {foo: "Hello", bar: "New", baz: "Bye"}

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#merge(**other : **U) forall U

Merges two named tuples into one, returning a new named tuple. If a key is defined in both tuples, the value and its type is used from other.

a = {foo: "Hello", bar: "Old"}
b = {bar: "New", baz: "Bye"}
a.merge(b) # => {foo: "Hello", bar: "New", baz: "Bye"}

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#pretty_print(pp)

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#size

Returns the number of elements in this named tuple.

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

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#sorted_keys

Returns a Tuple of symbols with the keys in this named tuple, sorted by name.

tuple = {foo: 1, bar: 2, baz: 3}
tuple.sorted_keys # => {:bar, :baz, :foo}

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#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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#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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#to_json(json : JSON::Builder)

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#to_s(io : IO) : Nil

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

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#values

Returns a Tuple with the values in this named tuple.

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

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