Oh, maybe you mistook reference type for the notion of reference. On Sunday, July 3, 2016 at 9:49:34 AM UTC+2, Martin Geisler wrote: > > Hi Chad, > > On Sat, Jul 2, 2016 at 10:43 AM, Chad <send...@gmail.com <javascript:>> > wrote: > > > > On Saturday, July 2, 2016 at 10:23:04 AM UTC+2, Martin Geisler wrote: > >> > >> On Fri, Jul 1, 2016 at 4:01 PM, Chad <send...@gmail.com> wrote: > >>> > >>> On Friday, July 1, 2016 at 3:44:10 PM UTC+2, Martin Geisler wrote: > >>>> I keep seeing references (hah!) to this concept of a "reference type" > >>>> :-) However, I just tried searching the language spec and Effective > Go > >>>> and there doesn't seem to be such a concept defined in those > >>>> documents. > >>> > >>> I think it should. It is mentioned here however > >>> https://blog.golang.org/go-maps-in-action > >> > >> You're right, that article calls maps, slices and pointers "reference > >> types". > >> > >> I feel that is a little unfortunate since it muddles the picture and > >> makes the implementation more obscure. I would have been happy to have > >> been told right from the start that a slice is a small struct, small > >> enough that you can pass it by value instead of with a pointer. That > >> allows me to build a mental model in terms of other Go constructs. > > > > > > A struct is considered a reference type if at least one of the field > > *points* to another object. (i.e. holds a reference to another object). > > https://en.wikipedia.org/wiki/Reference_type > > That is not how I've seen the word "reference type" used and I don't > think that's what the Wikipedia article tries to say. As I read it, it > says that a language like C++ has some types that are value types > (int, bool, structs, classes) and some types that are reference types > (&int, &bool). > > As far as I know, reference types only show up in function and method > signatures in C++. It specifies that the argument should be passed by > reference instead of being copied like normal -- the compiler will > typically handle this by changing the &int parameter to a *int (int > pointer) parameter, insert & at the call site and * inside the > function. So the reference type gives you almost the same as a > pointer, but without the explicit dereferencing. > > Other languages like Java and Python have reference types too: in > Java, all object instances are reference types. So when you pass an > object to a method, you pass a reference and modifications done in the > method are visible after the call. > > I believe C# allows you to specify if you want a class to be a > reference type or a value type. The Wikipedia article says you use > "struct" for value types and "class" for reference types. This matches > how "struct" gives you a value type in Go. > > The mail from as.utf8 points to this discussion (thanks!): > > https://groups.google.com/forum/m/#!topic/golang-dev/926npffb6lA > > which points to this issue: > > https://github.com/golang/go/issues/5083 > > They make it pretty clear that people have been trying to remove the > use of "reference type". > > > It's clearer. "small struct" would not be explicit enough nor true. > > I think that slices require typically more documentation effort to > clarify > > what they are. Then, the issue of comparability will be obvious. > > > > There are user-defined reference types too. > > > > type Foo struct{ > > name string > > data *[192]byte > > } > > > > That would be a reference type. This one is comparable. > > I don't think that's a reference type in the usual sense of the word. > The basic test for me is what happens when you pass a Foo to a > function: > > func ChangeTheFoo(f Foo) { > f.name = "changed" > } > > if the name field is changed after the call, then Foo is indeed a > reference type. However, it won't be changed in Go since the Foo > struct is copied when the function is called and this is why I say > that Foo is not a reference type. That is true of all structs in Go. > > -- > Martin Geisler >
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