Structures

Structures in Boa are similar to structures in C or Rust.

Simple example

Here is an example of a structure representing a 2-dimensional coordinate:

struct Point2D:
    x: i32
    y: i32

// OR

struct Point2D:
    x: i32, y: i32

// OR

struct Point2D: x: i32, y: i32

Note the absence of a comma when two fields of a structure are defined on two different lines.

Creating an instance of a structure

Creating an instance of a structure is done the same way as a function call:

let origin = Point2D(0, 0)

It is also possible to use the "named parameters" syntax:

let origin = Point2D(x=0, y=0)

Accessing and modifying structure fields

Use the . operator to access and modify the fields of an instance of a structure:

let some_point = Point2D(x=2, y=-1)
println(some_point.x)
some_point.x = 5

Recursive structures

In Boa, structs cannot contain directly or transitively a member whose type is the struct itself, because its size in memory would be infinite.

The two following examples are invalid:

struct DirectlyRecursive:
    recursive_field: DirectlyRecursive

struct IndirectlyRecursive:
    indirectly_recursive_field: AnotherStructure

struct AnotherStructure:
    inner: IndirectlyRecursive

The fix is simple: use a pointer to the recursive type instead of the recursive type itself.

struct Correct:
    correct: *Correct