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I am new to Go, and found it is OK to return the address of a local variable defined in a function. That is obviously not possible in C since local variable is in stack.
So I am just wondering why it is OK to do it in Go? In Go, the local variable is in heap? Will it affect performance since allocating heap memory is quite expensive than stack? Is it possible allocate local variable in stack in Go? Or actually is there stack memory in Go?
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The heap is a memory used by programming languages to store global variables. By default, all global variable are stored in heap memory space.
Go allocates memory in two places: a global heap for dynamic allocations and a local stack for each goroutine. Go prefers allocation on the stack — most of the allocations within a given Go program will be on the stack.
Java Heap space is used by java runtime to allocate memory to Objects and JRE classes. Whenever we create an object, it's always created in the Heap space.
Go values whose memory cannot be allocated this way, because the Go compiler cannot determine its lifetime, are said to escape to the heap. "The heap" can be thought of as a catch-all for memory allocation, for when Go values need to be placed somewhere.
General Memory Layout Each running program has its own memory layout, separated from other programs. The layout consists of a lot of segments, including: stack : stores local variables. heap : dynamic memory for programmer to allocate.
Anyways, it says "If you're familiar with operating system architecture, you might be interested to know that local variables and function arguments are stored on the stack, while global and static variables are stored on the heap."
There's a very clear answer to that question in the FAQ:
How do I know whether a variable is allocated on the heap or the stack?
From a correctness standpoint, you don't need to know. Each variable in Go exists as long as there are references to it. The storage location chosen by the implementation is irrelevant to the semantics of the language.
The storage location does have an effect on writing efficient programs. When possible, the Go compilers will allocate variables that are local to a function in that function's stack frame. However, if the compiler cannot prove that the variable is not referenced after the function returns, then the compiler must allocate the variable on the garbage-collected heap to avoid dangling pointer errors. Also, if a local variable is very large, it might make more sense to store it on the heap rather than the stack.
In the current compilers, if a variable has its address taken, that variable is a candidate for allocation on the heap. However, a basic escape analysis recognizes some cases when such variables will not live past the return from the function and can reside on the stack.
TLDR: You shouldn't care. Go takes care of allocation for you.
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