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Shapes

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

{symbol1: Type1, symbol2: Type2}

{'string1' => Type1, 'string2' => Type2}

This creates a fixed hash type (also referred to as a record), which is a hash with known keys and known types for each key. For example, {foo: String, bar: T.nilable(Float)} validates that an object is an hash with exactly those 2 keys as Ruby symbols, with foo being a String and bar being a Float or nil. For example: {foo: 'hello', bar: 3.14}.

Warning: Shape types have many known limitations, and should be considered an experimental feature. They may not work as expected or change without notice. For an alternative that plays better with static type checking, see Typed Structs.

##
# Shape types work for some simple cases,
# but have many known limitations.
#
# Consider instead using T::Struct to create a
# data class which models your domain.
#

extend T::Sig

sig {params(x: {a: Integer, b: String}).void}
def foo(x)
  # Limitation! returns T.untyped!
  T.reveal_type(x[:a]) # Revealed type: `T.untyped`

  # Limitation! does not warn when key doesn't exist!
  x[:c]
end

# --- What you expect ---
foo({a: 0,  b: ''}) # ok
foo({a: '', b: 0}) # error: type mismatch
foo({}) # error: missing keys

# --- What you might not expect ---
foo({a: 0, b: '', j: nil}) # ok

# --- Mutation: the ugly ---
y = {a: 0, b: ''}
y[:a] = '' # ok (!)

→ View on sorbet.run

sorbet internals note: the underlying() of a shape is an Hash where the key type is the union of all keys and the value type is the union of all the values.