On Friday, 17 April 2015 21:27:36 UTC+3, [email protected] wrote:
So it seems like you can stub out methods individually without having to
stub them all with what Paul suggested even on a single large interface. So
in this case I am still not sure what the individual interfaces serve?
These are two alternatives - you most likely wouldn't want to use those two

Small interfaces are obviously idiomatic, but their utility I thought came
in when functions only needed to take 1 or 2, out of the say 15 you split
out. If some method would need 10 out of them, them it seems unwieldy.
Wrapping those 10 up in another interface doesn't make sense because they
have no concept together. For example there is a lot of interface
composition in the io package, but you wouldn't make a
RunePipeReadWriterMtimeGetterCloser or something like that right?

I am also extremely curious about the intent behind embedding an interface
in a struct, which I can find almost zero information on. Embedding a
struct in a struct and an interface in an interface make total sense but an
interface in a struct does compile so there must be a purpose? Anyone? This
is driving my curiosity wild!
One recent example (note, code is WIP):

Essentially, I wanted to add separate the OAuth2 + routing logic from the
"Context" (which is intended mainly for setting up all the other services
rather than something by itself.)...

And it's much nicer to say:
sess.LoginURL... rather than sess.Context.LoginURL.

Similarly for your machine case... lets say you have

type Memory interface {
Store(dst uint32, value uint32)

type Machine struct {

machine := Machine{simplememory{}}

machine.Store(1, 1241)
machine.Memory.Store(1, 1241)

Basically, it allows you to compose a bigger thing out of smaller things -
with making it seem like a single thing.

Whether you want it to look as a single thing or not is a different
problem. e.g.

type V2 struct { X, Y int }

type Renderable interface {

type Entity struct {
Pos V2
Vel V2

func (e *Entity) Render(){ e.RenderAt(e.Pos) }

entity := Entity{V2{0,0}, V2{1,1}, NewTexture("example.png")}

Basically the main reason I can think of embedding an interfaces is to make
things look as a single cohesive thing without actually making them a
single thing.

For the background you're asking about, the Machine is the layer inbetween
different kinds of well, machines, that a single api will be built on top
of. Machines could be different os's or have different capabilities. That's
about all I can say on it, probably makes sense to have Machine be a
collection of components as things get larger, but this problem I am having
lies at the heart of that.

Thanks for the help!
On Friday, April 17, 2015 at 12:41:11 AM UTC-7, Egon wrote:
On Friday, 17 April 2015 09:04:55 UTC+3, [email protected] wrote:

Hey Egon, Yes those are the kinds of things in Machine, actions too like
ChangeRaid() or whatever. So this sounds like what Paul was suggesting but
how do the extra interfaces help? Could you guys point out some usages in
the standard lib maybe (or stdlib tests) which use interfaces embedded in
I don't know such examples in stdlib.

Maybe these help you out:

They also use interfaces a lot and are similar in building "machines".

The extra interfaces help, by being able to stub them out: e.g.

type Machine struct {

func TestCPU() {
m := Machine{CPU: NewCPU(), RAM: ramStub{}}
// ...

func TestMem() {
m := Machine{CPU: cpuStub(), RAM: NewRAM()}
// ...

Also could you elaborate more on the context. I mean I have no clue what
it is supposed to do (https://github.com/golang/go/wiki/howtoask).
Essentially you know what you are talking about and it seems like I got the
gist of it, but really I don't. (See Barnum effect)

Essentially... who will use the thing you build, where will it be used,
how is it valuable to the end user etc.

+ Egon
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