How Does Go Manage Stack vs. Heap Allocation of Structs and Garbage Collection?

Stack vs. Heap Allocation of structs in Go, and Their Relationship to Garbage Collection

In many programming languages, variables declared on the stack (automatic variables) have a finite lifetime, while those allocated on the heap (dynamic memory allocation) have a potentially unlimited lifetime. Go, however, presents a unique case where both stack-allocated and heap-allocated structs can persist beyond the scope of the function in which they were declared.

Question 1: Is example 2 declared on the stack or the heap?

Unlike in C or Python, in Go, taking the address of a local variable in a function does not necessarily mean that the variable resides on the stack. In both examples 1 and 2, the structs are allocated on the heap. This is determined through escape analysis, which evaluates whether a value escapes the scope of the current function. If it does, it must be stored on the heap to ensure its accessibility beyond the function's lifetime.

Question 2: How does example 2's struct stay available after the function returns?

Although the struct is allocated on the heap, it remains accessible after the function returns because Go's garbage collector ensures that the memory occupied by the struct is not released until it is no longer reachable by any living references.

Question 3: If example 2's struct is on the heap, why are structs passed by value instead of by reference?

Structs in Go are inherently passed by value. However, pointers to structs can be used to pass a reference to the struct. The use of pointers in this case is not to modify the struct, but rather to enable the ability to work with the struct's data indirectly, avoiding the cost of copying large structs.

In summary, Go's memory management system provides flexibility in allocating structs on the stack or heap, depending on their usage and accessibility requirements. The use of garbage collection ensures that both stack-allocated and heap-allocated structs are properly managed and reclaimed when they are no longer needed.

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