Joe, your question is perfectly answered by Axel.
I'll just share a few (personal) Go "style" comments:
Go likes you to test explicitly for failure where that is possible: did the
open fail, did the pipe break, etc.Multiple return values make this clear
by avoiding the need for a "reserved" error value of the normal-case return.
Go likes untested actions to work. In your case adding an existing key to a
map replaces the old entry, accessing a missing entry returns the default
value. ["no surprises"]
Go likes you to combine these approaches to make your own more elaborate
behaviors using the "comma OK" approach that Axel shared. In your case,
adding, and deleting could complain if there is already a matching entry,
or not a matching entry, or -- and this is the real reason -- by looking at
the payload of a new or matching entry to use application logic to decide
if that's ok or not. Only you can know so Go won't second guess you, and
the test-rather-than-panic style is because testing right there is deemed
the right way.
On Thu, Aug 13, 2020 at 11:42 AM 'Axel Wagner' via golang-nuts <
golang-nuts@googlegroups.com> wrote:
> No, there isn't, but you can check if the value exists:
>
> x, ok := m[k]
> if !ok {
> panic("does not exist")
> }
>
> You can also wrap that with methods, if you want to avoid the extra check.
>
> I disagree with you that panicking on a non-existent key is better -
> either in general, or in the majority of cases. Personally, I don't think I
> encountered many use-cases where the zero-value wasn't the perfect thing to
> use. I'm not saying your use-case doesn't exist or even that it's rare,
> just that I don't think you can generalize from your experience here.
>
> On Thu, Aug 13, 2020 at 8:36 PM Joe Marty <joe.ma...@smartersorting.com>
> wrote:
>
>> I'm very new to Go - apologies in advance if I'm missing something:
>>
>> I find it frustrating that there's no way to create a map that does *not*
>> automatically return a zero value for undefined key access by default.
>>
>> I love the fact that Go doesn't return "nil" for this use case (I love
>> Ruby, but I don't think they got that quite right), but returning a default
>> value is worse! It would make so much more sense if it would just panic
>> when accessing an undefined key. I'm not a Python guy, but I think this is
>> something Python got right.
>>
>> Creating a map that returns some default value when you access an
>> undefined key should be a special kind of map, or a special argument to
>> initializing the map (which Ruby does allow). In Go, is there even any way
>> to create a map that panics when you access an undefined key?
>>
>> -Joe
>>
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