Pointers vs. values in parameters and return values

Question

In Go there are various ways to return a struct value or slice thereof. For individual ones I\'ve seen:

type MyStruct struct {
    Val int
}

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Answer 1

A case where you generally need to return a pointer is when constructing an instance of some stateful or shareable resource. This is often done by functions prefixed with New.

Because they represent a specific instance of something and they may need to coordinate some activity, it doesn't make a lot of sense to generate duplicated/copied structures representing the same resource -- so the returned pointer acts as the handle to the resource itself.

Some examples:

• func NewTLSServer(handler http.Handler) *Server -- instantiate a web server for testing
• func Open(name string) (*File, error) -- return a file access handle

In other cases, pointers are returned just because the structure may be too large to copy by default:

• func NewRGBA(r Rectangle) *RGBA -- allocate an image in memory

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Alternatively, returning pointers directly could be avoided by instead returning a copy of a structure that contains the pointer internally, but maybe this isn't considered idiomatic:

• No such examples found in the standard libraries...
• Related question: Embedding in Go with pointer or with value