What does it mean that the value type belongs to the reference type?

The value of a value type copies when assigned or passed to a function, whereas a reference type is passed by reference, meaning a pointer to the existing instance is copied.

Value Types:

• Structures (struct)
• Enumerations (enum)
• Tuples (tuple)
• Most basic types (Int, String, Bool, Array, Dictionary, Set, etc.)

struct Point {
    var x: Int
    var y: Int
}

var p1 = Point(x: 1, y: 2)
var p2 = p1 // p1's value is copied to p2
p2.x = 10

// p1.x is still 1, p2.x is now 10
print("p1: \(p1.x)")
print("p2: \(p2.x)")

Reference Types:

• Classes (class)
• Functions (function closures)

class Coordinate {
    var x: Int
    var y: Int

    init(x: Int, y: Int) {
        self.x = x
        self.y = y
    }
}

var c1 = Coordinate(x: 1, y: 2)
var c2 = c1 // c2 references the same instance as c1
c2.x = 10

// c1.x is also now 10
print("c1: \(c1.x)")
print("c2: \(c2.x)")

Main differences:

Characteristic	Value Type	Reference Type
Assignment	Copies the value	Copies the reference (pointer)
Memory	Allocated on the stack (for simple cases)	Allocated on the heap
Sharing	Each variable has its own copy	Multiple variables can reference the same instance
Mutability	To modify, the copy must be modified	Changes via one reference are visible to all other references

In iOS development, both types are often used. Knowing their differences helps choose the appropriate type for a specific task and avoid unwanted side effects, especially when working with mutable data.