On Thu, Nov 21, 2019 at 10:25 AM Robert Engels <reng...@ix.netcom.com> wrote:
>
> I don't think we are talking about the same thing. You can certainly code an
> immutable object - just don't export any methods that mutate the object, nor
> export ANY fields.
Correct, we're talking about different things. The question is not
whether you can write an immutable object (yes you can), it is whether
there is a way to enforce the immutability of the receiver of a
method.
If the method is exported and if the receiver contains pointers, there
can be no guarantee that the method will not modify values reachable
from the copy of the receiver.
>
>
>
>
> -----Original Message-----
> >From: burak serdar <bser...@computer.org>
> >Sent: Nov 21, 2019 11:09 AM
> >To: Robert Engels <reng...@ix.netcom.com>
> >Cc: advanderv...@gmail.com, golang-nuts <golang-nuts@googlegroups.com>
> >Subject: Re: [go-nuts] Enforce immutability through static analysis
> >
> >On Thu, Nov 21, 2019 at 10:05 AM Robert Engels <reng...@ix.netcom.com> wrote:
> >>
> >> To clarify - the author of the package enforces immutability. With Go’s
> >> design this can be a simple comment on the field. The package shouldn’t be
> >> that large where this doesn’t work.
> >
> >The original problem remains: there is no way to enforce an immutable
> >receiver.
> >
> >>
> >> > On Nov 21, 2019, at 10:58 AM, Robert Engels <reng...@ix.netcom.com>
> >> > wrote:
> >> >
> >> >
> >> > Correct, but if the receiver method is mutating it, then it is not an
> >> > immutable object.
> >> >
> >> >
> >> >
> >> >
> >> > -----Original Message-----
> >> >> From: burak serdar <bser...@computer.org>
> >> >> Sent: Nov 21, 2019 10:53 AM
> >> >> To: Robert Engels <reng...@ix.netcom.com>
> >> >> Cc: advanderv...@gmail.com, golang-nuts <golang-nuts@googlegroups.com>
> >> >> Subject: Re: [go-nuts] Enforce immutability through static analysis
> >> >>
> >> >>> On Thu, Nov 21, 2019 at 9:49 AM Robert Engels <reng...@ix.netcom.com>
> >> >>> wrote:
> >> >>>
> >> >>> They can't unless the instance field is exported. Just hide it via
> >> >>> encapsulation with accessors.
> >> >>
> >> >> Can't do that with a receiver. All methods of a type are in the same
> >> >> package as the type, so all fields are visible to the receiver.
> >> >>
> >> >>
> >> >>>
> >> >>> -----Original Message-----
> >> >>> From: advanderv...@gmail.com
> >> >>> Sent: Nov 21, 2019 10:15 AM
> >> >>> To: golang-nuts
> >> >>> Subject: [go-nuts] Enforce immutability through static analysis
> >> >>>
> >> >>> Dear Gophers!
> >> >>>
> >> >>> I was wonder if it possible to force immutability on the method
> >> >>> receiver? I know Go doesn't support immutable types and that it is
> >> >>> possible to pass the receiver by value but if the receiver struct has
> >> >>> a field with a pointer type the method may still manipulate it:
> >> >>>
> >> >>> type Counter struct {
> >> >>> n *int
> >> >>> }
> >> >>>
> >> >>> func (c Counter) Render() string {
> >> >>> *c.n += 1
> >> >>> return strconv.Itoa(*c.n)
> >> >>> }
> >> >>>
> >> >>> I would like to force (or hint) the the user in writing interface{
> >> >>> Render() string } implementations that don't manipulate the method
> >> >>> receiver. So that they can be considered 'pure' in the functional
> >> >>> sense of the word and can be called repeatedly without side effects. I
> >> >>> would like the user to be able to define implementations of interface{
> >> >>> Render() string }such that I can safely call the method and use the
> >> >>> returned string to write a http.Reponse without it changing between
> >> >>> requests.
> >> >>>
> >> >>> I control the way in which Render is called and I am open to crazy
> >> >>> answers such as:
> >> >>>
> >> >>> - Maybe it is possible to use reflect to "switch" out the value
> >> >>> receiver for a temporary value which is discarded after every call?
> >> >>> - Maybe i can use static code analysis to warn the user? How feasible
> >> >>> is it to prevent all cases of this happening with just static code
> >> >>> analysis? can this be done at runtime?
> >> >>> - I could instead ask the user to provide a factory function that init
> >> >>> new Counters but maybe very inefficient if the structs are very large
> >> >>> (or have many nested structs)?
> >> >>>
> >> >>> Or maybe there is some possibility that I'm missing?
> >> >>>
> >> >>> Cheers,
> >> >>>
> >> >>> Ad
> >> >>>
> >> >>>
> >> >>> --
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> >> >>>
> >> >>>
> >> >>>
> >> >>>
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> >>
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