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|
# Every file should have a "typed sigil" that tells Sorbet how strict to be
# during static type checking.
#
# Strictness levels (lax to strict):
#
# ignore: Sorbet won't even read the file. This means its contents are not
# visible during type checking. Avoid this.
#
# false: Sorbet will only report errors related to constant resolution. This
# is the default if no sigil is included.
#
# true: Sorbet will report all static type errors. This is the sweet spot of
# safety for effort.
#
# strict: Sorbet will require that all methods, constants, and instance
# variables have static types.
#
# strong: Sorbet will no longer allow anything to be T.untyped, even
# explicitly. Almost nothing satisfies this.
# typed: true
# Include the runtime type-checking library. This lets you write inline sigs
# and have them checked at runtime (instead of running Sorbet as RBI-only).
# These runtime checks happen even for files with `ignore` or `false` sigils.
require 'sorbet-runtime'
module BasicSigs
# Bring in the type definition helpers. You'll almost always need this.
extend T::Sig
# Sigs are defined with `sig` and a block. Define the return value type with
# `returns`.
#
# This method returns a value whose class is `String`. These are the most
# common types, and Sorbet calls them "class types".
sig { returns(String) }
def greet
'Hello, World!'
end
# Define parameter value types with `params`.
sig { params(n: Integer).returns(String) }
def greet_repeat(n)
(1..n).map { greet }.join("\n")
end
# Define keyword parameters the same way.
sig { params(n: Integer, sep: String).returns(String) }
def greet_repeat(n, sep: "\n")
(1..n).map { greet }.join(sep)
end
# Notice that positional/keyword and required/optional make no difference
# here. They're all defined the same way in `params`.
# For lots of parameters, it's nicer to use do..end and a multiline block
# instead of curly braces.
sig do
params(
str: String,
num: Integer,
sym: Symbol,
).returns(String)
end
def uhh(str:, num:, sym:)
'What would you even do with these?'
end
# For a method whose return value is useless, use `void`.
sig { params(name: String).void }
def say_hello(name)
puts "Hello, #{name}!"
end
# Splats! Also known as "rest parameters", "*args", "**kwargs", and others.
#
# Type the value that a _member_ of `args` or `kwargs` will have, not `args`
# or `kwargs` itself.
sig { params(args: Integer, kwargs: String).void }
def no_op(*args, **kwargs)
if kwargs[:op] == 'minus'
args.each { |i| puts(i - 1) }
else
args.each { |i| puts(i + 1) }
end
end
# Most initializers should be `void`.
sig { params(name: String).void }
def initialize(name:)
# Instance variables must have annotated types to participate in static
# type checking.
# The value in `T.let` is checked statically and at runtime.
@upname = T.let(name.upcase, String)
# Sorbet can infer this one!
@name = name
end
# Constants also need annotated types.
SORBET = T.let('A delicious frozen treat', String)
# Class variables too.
@@the_answer = T.let(42, Integer)
# Sorbet knows about the `attr_*` family.
sig { returns(String) }
attr_reader :upname
sig { params(Integer).returns(Integer) }
attr_writer :write_only
# You say the reader part and Sorbet will say the writer part.
sig { returns(String) }
attr_accessor :name
end
module Debugging
extend T::Sig
# Sometimes it's helpful to know what type Sorbet has inferred for an
# expression. Use `T.reveal_type` to make type-checking show a special error
# with that information.
#
# This is most useful if you have Sorbet integrated into your editor so you
# can see the result as soon as you save the file.
sig { params(obj: Object).returns(String) }
def debug(obj)
T.reveal_type(obj) # Revealed type: Object
repr = obj.inspect
# Reminder that Ruby methods can be called without arguments, so you can
# save a couple characters!
T.reveal_type repr # Revealed type: String
"DEBUG: " + repr
end
end
module StandardLibrary
extend T::Sig
# Sorbet provides some helpers for typing the Ruby standard library.
# Use T::Boolean to catch both `true` and `false`.
#
# For the curious, this is equivalent to
# T.type_alias { T.any(TrueClass, FalseClass) }
sig { params(str: String).returns(T::Boolean) }
def confirmed?(str)
str == 'yes'
end
# Reminder that the value `nil` is an instance of NilClass.
sig { params(val: NilClass).void }
def only_nil(val:); end
# To avoid modifying standard library classes, Sorbet provides wrappers to
# support common generics.
#
# Here's the full list:
# * T::Array
# * T::Enumerable
# * T::Enumerator
# * T::Hash
# * T::Range
# * T::Set
sig { params(config: T::Hash[Symbol, String]).returns(T::Array[String]) }
def merge_values(config)
keyset = [:old_key, :new_key]
config.each_pair.flat_map do |key, value|
keyset.include?(key) ? value : nil
end
end
# Sometimes (usually dependency injection), a method will accept a reference
# to a class rather than an instance of the class. Use `T.class_of(Dep)` to
# accept the `Dep` class itself (or something that inherits from it).
class Dep; end
sig { params(dep: T.class_of(Dep)).returns(Dep) }
def dependency_injection(dep:)
dep.new
end
# Blocks, procs, and lambdas, oh my! All of these are typed with `T.proc`.
#
# Limitations:
# 1. All parameters are assumed to be required positional parameters.
# 2. The only runtime check is that the value is a `Proc`. The argument
# types are only checked statically.
sig do
params(
data: T::Array[String],
blk: T.proc.params(val: String).returns(Integer),
).returns(Integer)
end
def count(data, &blk)
data.sum(&blk)
end
sig { returns(Integer) }
def count_usage
count(["one", "two", "three"]) { |word| word.length + 1 }
end
# If the method takes an implicit block, Sorbet will infer `T.untyped` for
# it. Use the explicit block syntax if the types are important.
sig { params(str: String).returns(T.untyped) }
def implicit_block(str)
yield(str)
end
# If you're writing a DSL and will execute the block in a different context,
# use `bind`.
sig { params(num: Integer, blk: T.proc.bind(Integer).void).void }
def number_fun(num, &blk)
num.instance_eval(&blk)
end
sig { void }
def number_fun_usage(num)
number_fun(10) { puts digits.join }
end
# If the block doesn't take any parameters, don't include `params`.
sig { params(blk: T.proc.returns(Integer)).returns(Integer) }
def doubled_block(&blk)
2 * blk.call
end
end
module Combinators
extend T::Sig
# These methods let you define new types from existing types.
# Use `T.any` when you have a value that can be one of many types. These are
# sometimes known as "union types" or "sum types".
sig { params(num: T.any(Integer, Float)).returns(Integer) }
def hundreds(num)
num.round(-2)
end
# `T.nilable(Type)` is a convenient alias for `T.any(Type, NilClass)`.
sig { params(val: T.nilable(String)).returns(Integer) }
def strlen(val)
val.nil? ? -1 : val.length
end
# Use `T.all` when you have a value that must satisfy multiple types. These
# are sometimes known as "intersection types". They're most useful for
# interfaces (described later), but can also describe helper modules.
module Reversible
extend T::Sig
sig { void }
def reverse
# Pretend this is actually implemented
end
end
module Sortable
extend T::Sig
sig { void }
def sort
# Pretend this is actually implemented
end
end
class List
include Reversible
include Sortable
end
sig { params(list: T.all(Reversible, Sortable)).void }
def rev_sort(list)
# reverse from Reversible
list.reverse
# sort from Sortable
list.sort
end
def rev_sort_usage
rev_sort(List.new)
end
# Sometimes, actually spelling out the type every time becomes more confusing
# than helpful. Use type aliases to make them easier to work with.
JSONLiteral = T.type_alias { T.any(Float, String, T::Boolean, NilClass) }
sig { params(val: JSONLiteral).returns(String) }
def stringify(val)
val.to_s
end
end
module DataClasses
# Use `T::Struct` to create a new class with type-checked fields. It
# combines the best parts of the standard Struct and OpenStruct, and then
# adds static typing on top.
#
# Types constructed this way are sometimes known as "product types".
class Matcher < T::Struct
# Use `prop` to define a field with both a reader and writer.
prop :count, Integer
# Use `const` to only define the reader and skip the writer.
const :pattern, Regexp
# You can still set a default value with `default`.
const :message, String, default: 'Found one!'
# This is otherwise a normal class, so you can still define methods.
# You'll still need to bring `sig` in if you want to use it though.
extend T::Sig
sig { void }
def reset
self.count = 0
end
end
sig { params(text: String, matchers: T::Array[Matcher]).void }
def awk(text, matchers)
matchers.each(&:reset)
text.lines.each do |line|
matchers.each do |matcher|
if matcher.pattern =~ line
puts matcher.message
matcher.count += 1
end
end
end
end
# Gotchas and limitations
# 1. `const` fields are not truly immutable. They don't have a writer
# method, but may be changed in other ways.
class ChangeMe < T::Struct
const :list, T::Array[Integer]
end
def whoops!(change_me)
change_me = ChangeMe.new(list: [1, 2, 3, 4])
change_me.list.reverse!
change_me.list == [4, 3, 2, 1]
end
# 2. `T::Struct` inherits its equality method from `BasicObject`, which uses
# identity equality (also known as "reference equality").
class Position < T::Struct
const :x, Integer
const :y, Integer
end
def never_equal!
p1 = Position.new(x: 1, y: 2)
p2 = Position.new(x: 1, y: 2)
p1 != p2
end
# Define your own `#==` method to check the fields, if that's what you want.
class Position < T::Struct
# Note: reopened class
def ==(other)
self.class == other.class && self.x == other.x && self.y == other.y
end
end
# Use `T::Enum` to define a fixed set of values that are easy to reference.
# This is especially useful when you don't care what the values _are_ as much
# as you care that the set of possibilities is closed and static.
class Crayon < T::Enum
extend T::Sig
# Start initialization with `enum`.
enums do
# Define each member with `new`. Each of these is an instance of the
# `Crayon` class.
Red = new
Orange = new
Yellow = new
Green = new
Blue = new
Violet = new
Brown = new
Black = new
# The default value of the enum is its name in all-lowercase. To change
# that, pass a value to `new`.
Gray90 = new('light-gray')
end
# Define any aliases outside the initialization block.
Purple = Violet
sig { returns(String) }
def to_hex
case self
when Red then '#ff0000'
when Green then '#00ff00'
# ...
else '#ffffff'
end
end
end
sig { params(crayon: Crayon, path: T::Array[Point]).void }
def draw(crayon:, path:)
path.each do |point|
puts "(#{point.x}, #{point.y}) = " + crayon.to_hex
end
end
end
module FlowSensitivity
extend T::Sig
# Sorbet understands Ruby's control flow constructs and uses that information
# to get more accurate types when your code branches.
# You'll see this most often when doing nil checks.
sig { params(name: T.nilable(String)).returns(String) }
def greet_loudly(name)
if name.nil?
'HELLO, YOU!'
else
# Sorbet knows that `name` must be a String here, so it's safe to call
# `#upcase`.
"HELLO, #{name.upcase}!"
end
end
# The nils are a special case of refining `T.any`.
sig { params(id: T.any(Integer, T::Array[Integer])).returns(T::Array[String]) }
def database_lookup(id)
if id.is_a?(Integer)
# `ids` must be an Integer here.
[id.to_s]
else
# `ids` must be a T::Array[Integer] here.
id.map(&:to_s)
end
end
# Sorbet recognizes these methods that narrow type definitions:
# * is_a?
# * kind_of?
# * nil?
# * Class#===
# * Class#<
# * block_given?
#
# Because there so common, it also recognizes these Rails extensions:
# * blank?
# * present?
#
# Be careful to maintain Sorbet assumptions if you redefine these methods!
# Have you've ever written this line of code?
#
# raise StandardError, "Can't happen"
#
# Sorbet can help you prove that statically (this is known as
# "exhaustiveness") with `T.absurd`. It's extra cool when combined with
# `T::Enum`!
class Size < T::Enum
enums do
Byte = new('B')
Kibibyte = new('KiB')
Mebibyte = new('MiB')
# "640K ought to be enough for anybody"
end
sig { returns(Integer) }
def bytes
case self
when Byte then 1 << 0
when Kibibyte then 1 << 10
when Mebibyte then 1 << 20
else
# Sorbet knows you've checked all the cases, so there's no possible
# value that `self` could have here.
#
# But if you _do_ get here somehow, this will raise at runtime.
T.absurd(self)
# If you're missing a case, Sorbet can even tell you which one it is!
end
end
end
# Sorbet knows that no code can execute after a `raise` statement because it
# "never returns".
sig { params(num: T.nilable(Integer)).returns(Integer) }
def decrement(num)
raise ArgumentError, '¯\_(ツ)_/¯' unless num
num - 1
end
# You can annotate your own error-raising methods with `T.noreturn`.
class CustomError < StandardError; end
sig { params(message: String).returns(T.noreturn) }
def oh_no(message = 'A bad thing happened')
puts message
raise CustomError, message
end
# It also applies to infinite loops.
sig { returns(T.noreturn) }
def loading
loop do
%q(-\|/).each_char do |c|
print "\r#{c} reticulating splines..."
sleep 1
end
end
end
# You may run into a situation where Sorbet "loses" your type refinement.
# Remember that almost everything you do in Ruby is a method call that could
# return a different value next time you call it. Sorbet doesn't assume that
# any methods are pure (even those from `attr_reader` and `attr_accessor`).
sig { returns(T.nilable(Integer)) }
def answer
rand > 0.5 ? 42 : nil
end
sig { void }
def bad_typecheck
if answer.nil?
0
else
# But answer might return `nil` if we call it again!
answer + 1
end
end
sig { void }
def good_typecheck
ans = answer
if ans.nil?
0
else
# Now Sorbet knows that `ans` is non-nil.
ans + 1
end
end
end
module InheritancePatterns
extend T::Sig
# If you have a method that always returns the type of its receiver, use
# `T.self_type`. This is common in fluent interfaces and DSLs.
#
# Warning: This feature is still experimental!
class Logging
extend T::Sig
sig { returns(T.self_type) }
def log
pp self
self
end
end
class Data < Logging
extend T::Sig
sig { params(x: Integer, y: String).void }
def initialize(x: 0, y: '')
@x = x
@y = y
end
# You don't _have_ to use `T.self_type` if there's only one relevant class.
sig { params(x: Integer).returns(Data) }
def setX(x)
@x = x
self
end
sig { params(y: String).returns(Data) }
def setY(y)
@y = y
self
end
end
# Tada!
sig { void }
def chaining(data: Data)
data.setX(1).log.setY('a')
end
# If it's a class method (a.k.a. singleton method), use `T.attached_class`.
# No warning here. This one is stable!
class Box
extend T::Sig
sig { params(contents: String, weight: Integer).void }
def initialize(contents, weight)
@contents = contents
@weight = weight
end
sig { params(contents: String).returns(T.attached_class) }
def self.pack(contents)
new(contents, contents.chars.uniq.length)
end
end
class CompanionCube < Box
extend T::Sig
sig { returns(String) }
def pick_up
"♥#{@contents}🤍"
end
end
sig { returns(String) }
def befriend
CompanionCube.pack('').pick_up
end
# Sorbet has support for abstract classes and interfaces. It can check that
# all the concrete classes and implementations actually define the required
# methods with compatible signatures.
# Here's an abstract class:
class WorkflowStep
extend T::Sig
# Bring in the inheritance helpers.
extend T::Helpers
# Mark this class as abstract. This means it cannot be instantiated with
# `.new`, but it can still be subclassed.
abstract!
sig { params(args: T::Array[String]).void }
def run(args)
pre_hook
execute(args)
post_hook
end
# This is an abstract method, which means it _must_ be implemented by
# subclasses. Add a signature with `abstract` to an empty method to tell
# Sorbet about it.
#
# If this implementation of the method actually gets called at runtime, it
# will raise `NotImplementedError`.
sig { abstract.params(args: T::Array[String]).void }
def execute; end
# These methods _can_ be implemented by subclasses, but they're optional.
sig { void }
def pre_hook; end
sig { void }
def post_hook; end
end
class Configure < WorkflowStep
extend T::Sig
sig { void }
def pre_hook
puts 'Configuring...'
end
# To implement an abstract method, mark the signature with `override`.
sig { override.params(args: T::Array[String]).void }
def execute(args)
# ...
end
end
# And here's an interface:
module Queue
extend T::Sig
# Bring in the inheritance helpers.
extend T::Helpers
# Mark this module as an interface. This adds the following restrictions:
# 1. All of its methods must be abstract.
# 2. It cannot have any private or protected methods.
interface!
sig { params(num: Integer).void }
def push(num); end
sig { returns(T.nilable(Integer)) }
def pop; end
end
class PriorityQueue
extend T::Sig
# Include the interface to tell Sorbet that this class implements it.
# Sorbet doesn't support implicitly implemented interfaces (also known as
# "duck typing").
include Queue
sig { void }
def initialize
@items = []
end
# Implement the Queue interface's abstract methods. Remember to use
# `override`!
sig { override.params(num: Integer).void }
def push(num)
@items << num
@items.sort!
end
sig { override.returns(T.nilable(Integer)) }
def pop(num)
@items.shift
end
end
# If you use the `included` hook to get class methods from your modules,
# you'll have to use `mixes_in_class_methods` to get them to type-check.
module Mixin
extend T::Helpers
interface!
module ClassMethods
extend T::sig
sig { void }
def whisk
puts 'fskfskfsk'
end
end
mixes_in_class_methods(ClassMethods)
end
class EggBeater
include Mixin
end
EggBeater.whisk # Meringue!
end
module EscapeHatches
# Ruby is a very dynamic language, and sometimes Sorbet can't infer the
# properties you already know to be true. Although there are ways to rewrite
# your code so Sorbet can prove safety, you can also choose to "break out" of
# Sorbet using these "escape hatches".
# Once you start using `T.nilable`, Sorbet will start telling you _all_ the
# places you're not handling nils. Sometimes, you know a value can't be nil,
# but it's not practical to fix the sigs so Sorbet can prove it. In that
# case, you can use `T.must`.
sig { params(maybe_str: T.nilable(String)).returns(String) }
def no_nils_here(maybe_str)
# If maybe_str _is_ actually nil, this will error at runtime.
str = T.must(maybe_str)
str.downcase
end
# More generally, if you know that a value must be a specific type, you can
# use `T.cast`.
sig do
params(
str_or_ary: T.any(String, T::Array[String]),
idx_or_range: T.any(Integer, T::Range[Integer]),
).returns(T::Array[String])
end
def slice2(str_or_ary, idx_or_range)
# Let's say that, for some reason, we want individual characters from
# strings or sub-arrays from arrays. The other options are not allowed.
if str_or_ary.is_a?(String)
# Here, we know that `idx_or_range` must be a single index. If it's not,
# this will error at runtime.
idx = T.cast(idx_or_range, Integer)
[str_or_ary.chars.fetch(idx)]
else
# Here, we know that `idx_or_range` must be a range. If it's not, this
# will error at runtime.
range = T.cast(idx_or_range, T::Range[Integer])
str_or_ary.slice(range) || []
end
end
# If you know that a method exists, but Sorbet doesn't, you can use
# `T.unsafe` so Sorbet will let you call it. Although we tend to think of
# this as being an "unsafe method call", `T.unsafe` is called on the receiver
# rather than the whole expression.
sig { params(count: Integer).returns(Date) }
def the_future(count)
# Let's say you've defined some extra date helpers that Sorbet can't find.
# So `2.decades` is effectively `(2*10).years` from ActiveSupport.
Date.today + T.unsafe(count).decades
end
# If this is a method on the implicit `self`, you'll have to make that
# explicit to use `T.unsafe`.
sig { params(count: Integer).returns(Date) }
def the_past(count)
# Let's say that metaprogramming defines a `now` helper method for
# `Time.new`. Using it would look like this:
#
# now - 1234
T.unsafe(self).now - 1234
end
# There's a special type in Sorbet called `T.untyped`. For any value of this
# type, Sorbet will allow it to be used for any method argument and receive
# any method call.
sig { params(num: Integer, anything: T.untyped).returns(T.untyped) }
def nothing_to_see_here(num, anything)
anything.digits # Is it an Integer...
anything.upcase # ... or a String?
# Sorbet will not be able to infer anything about this return value because
# it's untyped.
BasicObject.new
end
def see_here
# It's actually nil! This will crash at runtime, but Sorbet allows it.
nothing_to_see_here(1, nil)
end
# For a method without a sig, Sorbet infers the type of each argument and the
# return value to be `T.untyped`.
end
# The following types are not officially documented but are still useful. They
# may be experimental, deprecated, or not officially unsupported.
module ValueSet
# A common pattern in Ruby is to have a method accept one value from a set of
# options. Especially when starting out with Sorbet, it may not be practical
# to refactor the code to use `T::Enum`. In this case, you can use `T.enum`.
#
# Note: Sorbet can't check this statically becuase it doesn't track the
# values themselves.
sig do
params(
data: T::Array[Numeric],
shape: T.enum([:circle, :square, :triangle])
)
end
def plot_points(data, shape: :circle)
data.each_with_index do |y, x|
puts "#{x}: #{y}"
end
end
end
module Generics
# Generics are useful when you have a class whose method types change based
# on the data it contains or a method whose method type changes based on what
# its arguments are.
# A generic method uses `type_parameters` to declare type variables and
# `T.type_parameter` to refer back to them.
sig do
type_parameters(:element)
.params(
element: T.type_parameter(:element),
count: Integer,
).returns(T::Array[T.type_parameter(:element)])
end
def repeat_value(element, count)
count.times.each_with_object([]) do |elt, ary|
ary << elt
end
end
sig do
type_parameters(:element)
.params(
count: Integer,
block: T.proc.returns(T.type_parameter(:element)),
).returns(T::Array[T.type_parameter(:element)])
end
def repeat_cached(count, &block)
elt = block.call
ary = []
count.times do
ary << elt
end
ary
end
# A generic class uses `T::Generic.type_member` to define type variables that
# can be like regular type names.
class BidirectionalHash
extend T::Generic
Left = type_member
Right = type_member
sig { void }
def initialize
@left_hash = T.let({}, T::Hash[Left, Right])
@right_hash = T.let({}, T::Hash[Right, Left])
end
# Implement just enough to make the methods below work.
sig { params(lkey: Left).returns(T::Boolean) }
def lhas?(lkey)
@left_hash.has_key?(lkey)
end
sig { params(rkey: Right).returns(T.nilable(Left)) }
def rget(rkey)
@right_hash[rkey]
end
end
# To specialize a generic type, use brackets.
sig do
params(
options: BidirectionalHash[Symbol, Integer],
choice: T.any(Symbol, Integer),
).returns(T.nilable(String))
end
def lookup(options, choice)
case choice
when String
options.lhas?(choice) ? choice.to_s : nil
when Integer
options.rget(choice)
else
T.absurd(choice)
end
end
# To specialize through inheritance, re-declare the `type_member` with `fixed`.
class Options < BidirectionalHash
Left = type_member(fixed: Symbol)
Right = type_member(fixed: Integer)
end
sig do
params(
options: Options,
choice: T.any(Symbol, Integer),
).returns(T.nilable(String))
end
def lookup2(options, choice)
lookup(options, choice)
end
# There are other variance annotations you can add to `type_member`, but
# they're rarely used.
end
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