Hi Chad, On Sat, Jul 2, 2016 at 10:43 AM, Chad <send2b...@gmail.com> 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 -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
