What exactly does a variable store when we create an object of type value?

When we create an object of type value (structure, enumeration, tuple in Swift), the variable stores a copy of the data of this object directly in memory. Assignment or passing such an object by parameter results in copying its contents.

Examples:

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

var p1 = Point(x: 1, y: 2) // Variable p1 stores a copy of the data (x=1, y=2)
var p2 = p1              // p2 gets a copy of p1's data. These are independent copies.

p1.x = 10                // Only p1.x changes
print(p2.x)              // Will output 1, since p2 did not change

Comparison with reference type (class):

Characteristic	Value Type (structure, enum)	Reference Type (class)
What is stored in the variable	A copy of the object data	A reference to the object in memory
Assignment / Passing	Copying data	Copying the reference (points to the same object)
Modification	Affects only the current copy	Affects the object the reference points to (may affect other variables referencing the same object)