What does it mean that references are stored on the stack?

Local variable-values (types Int, Bool, Double, String, Struct, Enum) created inside a function are stored on the stack. The stack is a memory area used for local variables, function parameters, and return addresses. It operates on a LIFO (Last In, First Out) principle.

Working principle:

1. Placement: When a function is called, a stack frame is created. The local variable-values of this function are placed in this frame.
2. Access: Access to variables on the stack is very fast because their addresses are determined relative to the stack pointer.
3. Deallocation: When the function completes, its stack frame (and all variables stored in it) is simply removed from the top of the stack.

Example:

func processNumbers() {
    var number1: Int = 10 // number1 is stored on the stack
    let number2: Double = 20.5 // number2 is stored on the stack
    
    // ... use of number1 and number2
} // When exiting the processNumbers function, number1 and number2 are removed from the stack

Unlike reference types (Class, Actor), whose instances are stored in the heap, and only a reference to this instance is stored on the stack.