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Language Reference

Standard Library

Compiler design

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Learning path

Learning path

Write and run a program

01 Program entry

02 Explicit types and assignment

03 Type inference

04 String interpolation

05 Operators and comparisons

06 Conditional execution

Organize calculations with functions

07 Functions and explicit returns

08 Named arguments

09 Default arguments

10 Argument shorthand

11 if as a result

12 Final-expression returns

Work with collections and control flow

13 Lists

14 Iteration

15 Conditional loops

16 Break

17 Continue

18 Arrays

19 Maps

20 Sets

21 Collection value semantics

22 Collection `for` elements

23 Collection `if` elements

24 Spread in collections

Model values and entities

25 Value declarations

26 Value equality

27 Class declarations

28 Class identity

29 Copying a class

30 Explicit constructors

31 Computed properties

32 Fluent methods

Handle absence and match states

33 Nullable values

34 Flow narrowing

35 Safe access

36 Null fallback

37 Plain enums

38 Data enums

39 Switch results

40 Exhaustive matching

41 Nested patterns

Compose abstractions

42 Interface declarations

43 Implementing an interface

44 Default interface methods

45 Class inheritance

46 Overriding methods

47 Generic types

48 Generic functions

49 Generic inference

50 Matching generic types

51 Function overloads

Functions as values

52 Function values

53 Lambdas

54 Capturing values

55 Bound method references

56 Extension functions

57 Trailing callbacks

58 Named callback parameters

59 Chaining block calls

Build a project

60 Imports

61 Modules

62 Packages

63 Visibility

64 Local dependencies

65 Tests

66 Exception handling

67 Cleanup with finally

Describe declarations

68 Type declaration references

69 Field declaration references

70 Function declaration references

71 Annotation targets

72 Annotation retention

73 Runtime annotation metadata

74 Function interception

75 Interceptor entry and exit

76 Documenting declarations for agents

Observe and build

77 Lexical references

78 Field handles

79 Field subscriptions

80 Collection change notifications

81 Resource ownership

82 Result builders

83 Control flow in result builders

Use libraries

84 JSON value roundtrip

85 Writing and reading a file

86 Typed file failures

87 A packaged library

On this page

Nullability

Learn each feature in an independent, runnable lesson:

33 Nullable values
34 Flow narrowing
35 Safe access
36 Null fallback

For complete semantics, see the Language Reference.

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