1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
|
# 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'
class 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_2(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(write_only: 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 : 'sensible default'
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 { params(num: Integer).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(Rational) }
def hundreds(num)
num.rationalize
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
extend T::Sig
# 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
Kernel.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
sig { params(change_me: ChangeMe).returns(T::Boolean) }
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 Coordinate < T::Struct
const :row, Integer
const :col, Integer
end
sig { returns(T::Boolean) }
def never_equal!
p1 = Coordinate.new(row: 1, col: 2)
p2 = Coordinate.new(row: 1, col: 2)
p1 != p2
end
# Define your own `#==` method to check the fields, if that's what you want.
class Position < T::Struct
extend T::Sig
const :x, Integer
const :y, Integer
sig { params(other: Object).returns(T::Boolean) }
def ==(other)
# There's a real implementation here:
# https://github.com/tricycle/sorbet-struct-comparable
true
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
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[Position]).void }
def draw(crayon:, path:)
path.each do |pos|
Kernel.puts "(#{pos.x}, #{pos.y}) = " + crayon.to_hex
end
end
# To get all the values in the enum, use `.values`. For convenience there's
# already a `#serialize` to get the enum string value.
sig { returns(T::Array[String]) }
def crayon_names
Crayon.values.map(&:serialize)
end
# Use the "deserialize" family to go from string to enum value.
sig { params(name: String).returns(T.nilable(Crayon)) }
def crayon_from_name(name)
if Crayon.has_serialized?(name)
# If the value is not found, this will raise a `KeyError`.
Crayon.deserialize(name)
end
# If the value is not found, this will return `nil`.
Crayon.try_deserialize(name)
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 they're 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
extend T::Sig
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
# We're gonna need `puts` and `raise` for this next part.
include Kernel
# 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
# ^ Method + does not exist on NilClass component of T.nilable(Integer)
end
end
sig { void }
def good_typecheck
ans = answer
if ans.nil?
0
else
# This time, 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 { params(data: Data).void }
def chaining(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(args); 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 { abstract.params(num: Integer).void }
def push(num); end
sig { abstract.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 = T.let([], T::Array[Integer])
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
@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
'fskfskfsk'
end
end
mixes_in_class_methods(ClassMethods)
end
class EggBeater
include Mixin
end
EggBeater.whisk # Meringue!
end
module EscapeHatches
extend T::Sig
# 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
extend T::Sig
# 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])
).void
end
def plot_points(data, shape: :circle)
data.each_with_index do |y, x|
Kernel.puts "#{x}: #{y}"
end
end
end
module Generics
extend T::Sig
# 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::Sig
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 Symbol
options.lhas?(choice) ? choice.to_s : nil
when Integer
options.rget(choice).to_s
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
|