bear/examples/structs.vr

// structs.vr — struct/record values with field access.
//   vr run examples/structs.vr

fn make_point(x, y) {
	return { x: x, y: y }
}

fn dist_sq(p) {
	return p.x * p.x + p.y * p.y
}

fn main() {
	// struct literal: { name: value, ... }
	let p = { name: "bob", age: 30 }
	println(p)          // {name: bob, age: 30}
	println(p.name)     // bob
	println(p.age)      // 30

	// field assignment mutates the record
	p.age = 31
	println(p.age)      // 31

	// structs are reference values, like arrays
	let q = p
	q.age = 40
	println(p.age)      // 40 — p and q share the same record

	// structs flow through functions
	let pt = make_point(3, 4)
	println(dist_sq(pt)) // 25

	// structs compose with arrays, in both directions
	let pts = [{ x: 1, y: 2 }, { x: 10, y: 20 }]
	println(pts[1].x)   // 10
	pts[0].x = 99
	println(pts[0].x)   // 99

	let person = { name: "amy", addr: { city: "nyc", zip: 10001 } }
	println(person.addr.city) // nyc
	person.addr.zip = 90001
	println(person.addr.zip)  // 90001

	let holder = { items: [1, 2, 3] }
	holder.items[1] = 42
	println(holder.items) // [1, 42, 3]

	// records can be built incrementally from an empty struct
	let s = {}
	s.kind = "point"
	s.value = 7
	println(s)          // {kind: point, value: 7}

	// structs compare by identity with == / !=
	let a = { n: 1 }
	let b = a
	let c = { n: 1 }
	assert a == b
	assert a != c
}