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