On Thu, Aug 27, 2020 at 10:06 AM targe...@gmail.com <target....@gmail.com> wrote:
> Not sure if it was mentioned here, but IMO the main issues isn't nil data > itself, but how easy it's created. It'd be much less of a surprise if > creating nil-data required explicit cast from nil struct pointer to > interface pointer and resulted in just nil interface pointer in case of > implicit cast. Though such change is almost certainly breaking one. > This would require to insert extra nil-checks when assigning a pointer-value to an interface, as the compiler can't know if a pointer is nil or not. Personally, I would also find it very confusing, if converting a T to a T changed program behavior (though arguably, there is one such case currently with `uintptr(uintptr(unsafe.Pointer))`. But usage of `unsafe` seems sufficiently advanced). > > On Monday, August 24, 2020 at 7:08:17 AM UTC+3 alex.be...@gmail.com wrote: > >> Can we at least move with the https://github.com/golang/go/issues/22729 >> , please? Anything will help with the current mess. >> >> >> On Sunday, August 23, 2020 at 8:52:30 PM UTC-7, Ian Lance Taylor wrote: >> >>> On Sun, Aug 23, 2020 at 1:16 PM Denis Cheremisov >>> <denis.c...@gmail.com> wrote: >>> > >>> > You may use something like this >>> > >>> > value2 := >>> *(*uint64)(unsafe.Pointer(uintptr(unsafe.Pointer(&value)) + 8)) >>> > if value2 == 0 { >>> > return true >>> > } >>> > >>> > on AMD64, should work also for any 64 bit architecture (at least I >>> believe so). Remember though this is hacky and may stop working once. >>> >>> You could do that, but please don't. >>> >>> Ian >>> >>> >>> > воскресенье, 23 августа 2020 г. в 22:58:51 UTC+3, Aviv Eyal: >>> >> >>> >> I was trying to show that the current behavior is confusing and that >>> fmt.Print() needing to resort to panic-and-recover is kinda code smell, but >>> I sorts-of convinced myself that the current behavior is right, or at least >>> consistent. >>> >> >>> >> In my code, I got bit because I sometimes use v *Type to denote "I >>> may or may not have a value here" (where Type is a value-type). >>> >> This is probably a bad practice on my behalf, because I break the >>> Liskov substitution principle: there is a value of `*Type` that is not a >>> valid value of `Type`, and I let this value slip by. >>> >> >>> >> In this case, `v Type` implements Stringer (i.e. valid callee for >>> `v.String()`, but `v *Type`, in the strictest sense, does not. >>> >> The only reason we can write: >>> >> >>> >> func (Type) String() string {...} >>> >> v *Type = &Type{...} >>> >> _ = v.String() >>> >> >>> >> and have it compile, is syntactic sugar: `v` gets implicitly >>> de-referenced, and there's an implicit assumption that it's not nil. >>> >> And there's a matching syntactic sugar for converting `Type` to a >>> `*Type`. >>> >> >>> >> So, In the code: >>> >> >>> >> func (Type) String() string {...} >>> >> >>> >> v *Type = nil >>> >> r interface{} = v >>> >> _, ok = r.(Stringer) >>> >> >>> >> What I really want to ask is "Can I, at runtime, call r.String()?", >>> whereas the question Go answers is "Is any of `r`, `*r`, or `&r` defines >>> .String()?" - which matches the static semantics of `r.String()`. >>> >> >>> >> So, while I should probably not use *Type as a replacement for >>> Optional<Type>, I think it might make sense to have some operator that can >>> determine, at run-time, if a call `r.String()` is valid (including a >>> nil-check). >>> >> >>> >> >>> >> -- Aviv >>> >> >>> >> On Saturday, April 11, 2020 at 4:48:28 PM UTC+3 ren...@ix.netcom.com >>> wrote: >>> >>> >>> >>> I agree with the OP. The usefulness of nil interfaces is pretty >>> limited. Show me a useful case that cant easily be implemented with non-nil >>> interfaces. >>> >>> >>> >>> I would argue that allowing nil interfaces causes more subtle latent >>> bugs and makes it harder to reason about the correctness of code when >>> reviewing it. >>> >>> >>> >>> It just feels wrong. I realize I’m probably in the minority here but >>> the OP is not alone. >>> >>> >>> >>> On Apr 11, 2020, at 8:20 AM, 'Axel Wagner' via golang-nuts < >>> golan...@googlegroups.com> wrote: >>> >>> >>> >>> On Fri, Apr 10, 2020 at 7:17 PM <cpu...@gmail.com> wrote: >>> >>>> >>> >>>> I realize I'm reviving an age-old discussion here and apologize for >>> bringing up the undead. I happend to run into this when my application >>> panicked when some interfaces where initialized with nil mock objects >>> instead of being left uninitialized as in production mode. >>> >>> >>> >>> >>> >>> Let's imagine a world in which `foo == nil` also is true if `foo` is >>> an interface-value containing a nil-pointer. Let's say in this world, >>> someone sends a message to golang-nuts. They wrote a mock for the same >>> code. And since it's just a mock, they just returned static value from its >>> methods and didn't need to care if the pointer was nil or not. They are >>> confused, because the passed in this mock, but the code just assumed the >>> field was uninitialized and never called into their mock. What would you >>> tell them? Why is their confusion less valid? >>> >>> >>> >>>> This would be an example where a nil implementing fooer is never >>> caught: >>> >>>> >>> >>>> type fooer interface { >>> >>>> foo() >>> >>>> } >>> >>>> >>> >>>> type other struct{} >>> >>>> >>> >>>> func (o *other) foo() {} // implement fooer >>> >>>> >>> >>>> func main() { >>> >>>> var f fooer >>> >>>> >>> >>>> var p *other // nil >>> >>>> f = p // it is a fooer so I can assign it >>> >>>> >>> >>>> if f == nil { >>> >>>> // will not get here >>> >>>> } >>> >>>> } >>> >>>> >>> >>>> >>> >>>> My confusion comes from the point that the nil interface is >>> apparently not "a nil-pointer with the correct method set" while *other is >>> even if nil. >>> >>> >>> >>> >>> >>> In the code you posted, even a nil *other is a perfectly fine >>> implementation of fooer. You can call `(*other)(nil).foo()` without any >>> problems. >>> >>> So, as you illustrated, calling methods on a nil-pointer can be >>> totally fine. A nil-interface, OTOH, doesn't have any methods to call, as >>> it doesn't contain a dynamic value. If you write `(*other)(nil).foo()`, it >>> is completely clear what code gets called - even if that code *might* >>> panic. If you write `fooer(nil).foo()`, what code should be called in your >>> opinion? >>> >>> >>> >>> I think it's easy to see that a nil-interface and a nil-pointer >>> stored in an interface are very different things. Even from first >>> principles, without deep knowledge of the language. And if they are >>> obviously different, I don't understand why you'd find it confusing that >>> they are not the same in this particular manner. >>> >>> >>> >>>> The above is a case where that might happen. In can be worked >>> around but it is unexpected unless the programmer is deeply rooted in the >>> language definition. >>> >>> >>> >>> >>> >>> I fully agree with that. What I *don't* agree with, is where you >>> attribute the problem here. You say, the problem is that the nil-check is >>> ill-behaved. I say that - if anything - the original nil-assignment is >>> ill-behaved. Having `(fooer)((*other)(nil)) == nil` be true is semantically >>> wrong, because by checking against `nil`, you are checking if you have a >>> correct implementation - and you might well have a correct implementation, >>> even if it's using a nil-pointer. >>> >>> >>> >>> Note, that the contained pointer being nil isn't the *only* case in >>> which calling the method might panic. For example, what about this code? >>> >>> https://play.golang.org/p/lNq0qphez7v >>> >>> Shouldn't the `nil`-check also catch that? After all, calling the >>> method panics, so it's clearly not a valid implementation - even if x >>> itself is not nil. Why is a nil-pointer more special than any other value >>> that causes a method to panic? >>> >>> >>> >>>> Seems as of today that there is no tooling to support that check. >>> Maybe it's not a widespread issue. >>> >>> >>> >>> >>> >>> As of today, the language also isn't changed :) Maybe someone who >>> think this is important enough to change the language, could also feel it's >>> important enough to write this tooling. >>> >>> >>> >>>> >>> >>>> -- >>> >>>> 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...@googlegroups.com. >>> >>>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/e0dbcd38-510e-43b9-b363-2af1c636250b%40googlegroups.com. >>> >>> >>> >>> >>> -- >>> >>> 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...@googlegroups.com. >>> >>> >>> >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/CAEkBMfEPjcsZ3enqXyt%2BUphFJ1cNQ81cFCcjfwwkQZKHMrjSzA%40mail.gmail.com. >>> >>> > >>> > -- >>> > 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 golan...@googlegroups.com. >>> >> > To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/c1ed2e38-6215-4ed2-8357-f8b5d83bf1a7n%40googlegroups.com. >>> >>> >> -- > 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. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/84244528-84e6-4c2e-89bf-7fbf0590e132n%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/84244528-84e6-4c2e-89bf-7fbf0590e132n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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