Can Go Functions Safely Return Pointers to Local Structs?

Returning a Pointer to a Local Struct in Go

In Go, it's possible to create functions that return pointers to local structs. This may seem like an erroneous construct in languages like C , but the semantics in Go differ significantly.

Pointer Escape Analysis

Go utilizes pointer escape analysis to determine how to allocate objects. When a function returns a pointer to a local variable, the compiler performs escape analysis to assess whether that pointer can escape the function's scope.

If Pointer Escapes

If the pointer escapes the local stack, indicating that it's accessible outside the function, the object is allocated on the heap using the new keyword. This ensures that the object's lifetime extends beyond the function's execution and can be accessed by other parts of the program.

If Pointer Stays Local

Conversely, if the pointer doesn't escape the local function, the compiler may allocate the object on the stack. This is an optimization that reduces memory overhead and potentially improves performance. However, it's important to note that the compiler isn't obligated to do this. If the pointer escape analysis cannot conclusively determine that the pointer stays local, it may still allocate the object on the heap for safety reasons.

Example

Consider the following Go code:

type Point struct {
  x, y int
}

func NewPoint() *Point {
  return &Point{10, 20}
}

In this example, the NewPoint function returns a pointer to a locally defined Point struct. The pointer escape analysis will determine whether the pointer escapes the function's scope. If it escapes, the Point struct will be allocated on the heap; otherwise, it may be allocated on the stack.

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