tuples.md

id	title
tuples	Tuples

TODO: This page is still a fragment. Contributions welcome!

[Type1, Type2, ...]

This creates a fixed array type (also referred to as a tuple), which is a fixed-length array with known types for each element. For example, [String, T.nilable(Float)] validates that an object is an array of exactly length 2, with the first item being a String and the second item being a Float or nil.

Warning: Tuples have many known limitations, and should be considered an experimental feature. They may not work as expected or change without notice.

##
# Tuple types work for some simple cases,
# but have many known limitations.
#

extend T::Sig

sig {params(x: [Integer, String]).returns(Integer)}
def foo(x)
  T.reveal_type(x[0]) # Revealed type: `Integer`
end

# --- What you expect ---
foo([0, '']) # ok
foo(['', 0]) # error: type mismatch
foo([]) # error: not right tuple type

# --- What you might not expect ---
foo([0, '', nil]) # ok

# --- Mutation: the ugly ---
y = [0, '']
y[0] = '' # ok (!)
T.reveal_type(y[0]) # Reveal type: `Integer(0)` (!!)

# --- Flow-sensitivity: even uglier ---
y_0 = y[0]
if y_0.is_a?(String)
  puts y_0 # error: This code is unreachable (!!!)
end

→ View on sorbet.run

sorbet internals note: the underlying of a tuple is an Array of the union of each element type.