6.10 Mutable Variables and Assignment

8.12

6.10 Mutable Variables and Assignment🔗ℹ

binding operator

maybe_annot	=	:: annot
	\|	:~ annot
	\|	ϵ

Binds id so that its value can be changed using an assignment operator such as :=.

If an annot is present using ::, then the value of every assignment to id must satisfy the annotation, and the value installed into id is the converted value if annot is a converter annotation. Static information from annot is associated with uses of id whether attached by :: or :~.

> def mutable count = 0
> count := count + 1
> count
1
> count := "string"

> def mutable count :: Int = 0
> count := count + 1
> count := "string"
count: value does not satisfy annotation
value: "string"
annotation: Int

expression

id := expr

An assignment operator that changes the value of id to the result of expr and returns #void. The id must be bound with mutable.

The := operator is also recognized by other forms, such as . and #%index, for changing mutable components of some values.

> def mutable count = 0
> count := count + 1
> count
1

1	Rhombus Essentials
2	Collections and Iteration
3	Syntax Objects and Macros
4	Classes and Interfaces
5	Static Information and Binding
6	Core Reference
7	Meta and Macros Reference
8	Rhombus Static by Default
9	Libraries
10	Naming Conventions

6.1	General Forms
6.2	Definitions
6.3	Namespaces
6.4	Import
6.5	Export
6.6	Functions
6.7	Operators
6.8	Classes and Interfaces
6.9	Veneers
6.10	Mutable Variables and Assignment
6.11	Repetitions
6.12	Block
6.13	Conditionals
6.14	Matching
6.15	Iteration
6.16	Recursion
6.17	Context Parameters
6.18	Exceptions
6.19	Continuations
6.20	Implicit Forms
6.21	Static and Dynamic Lookup
6.22	Modules and Submodules
6.23	Booleans
6.24	Numbers
6.25	Characters
6.26	Strings
6.27	Keywords
6.28	Symbols
6.29	Byte Strings
6.30	Lists
6.31	Pairs and Pair Lists
6.32	Mutable Lists
6.33	Arrays
6.34	Maps
6.35	Sets
6.36	Boxes
6.37	Indexables
6.38	Listables
6.39	Sequences
6.40	Appendables
6.41	Comparables
6.42	Paths
6.43	Source Locations
6.44	Void
6.45	Equality
6.46	Dot
6.47	Multiple Values
6.48	Annotations
6.49	Enumerations
6.50	Input and Output
6.51	Eval
6.52	Syntax Objects
6.53	Syntax Classes
6.54	Simple Expression Macros
6.55	Unit Testing