How is it determined where memory is allocated — on the stack or in the heap?

In Go, memory is allocated either on the stack or in the heap, depending on how the variable is used and how the compiler analyzes its lifecycle.

• Stack — used for local variables that live within a function and do not go beyond its scope. Memory on the stack is allocated quickly and automatically freed when the function exits.

• Heap — used for variables that need to live longer than the function call, or when the size of data is unknown at compile time. Memory in the heap is allocated dynamically and requires garbage collection for freeing.

The Go compiler applies escape analysis — an analysis that determines whether a variable "escapes" the function. If a variable "escapes" (for example, returned from a function or stored in a global structure), it is allocated in the heap. If not — on the stack.

Example:

func foo() *int {
    x := 10
    return &x // x "escapes" from the function, allocated in the heap
}

func bar() {
    y := 20 // y is local, allocated on the stack
    fmt.Println(y)
}

Thus, the decision to allocate memory is made by the compiler based on code analysis to optimize performance and memory management.