On Jun 20, 2017 3:40 PM, "Ian Lance Taylor" <i...@golang.org> wrote:
On Mon, Jun 19, 2017 at 11:30 PM, Will Hawkins <hawki...@borlaugic.com>
wrote:
>
> On Tuesday, June 20, 2017 at 2:19:25 AM UTC-4, Volker Dobler wrote:
>>
>> On Tuesday, 20 June 2017 06:52:58 UTC+2, Will Hawkins wrote:
>>>
>>> I know that there is a difference between interface values and dynamic
>>> types and dynamic values. Is it possible that the documentation about
the %T
>>> is misleading? Should it be more specific that it returns the variable's
>>> "dynamic type."
>>> [...]
>>>
>>> Should the documentation for %T be updated to say that it prints the
>>> variable's dynamic type?
>>
>>
>> Well, no.
>> Look at fmt.Printf: It take a format string and a bunch of interface{}
>> values to
>> be printed. If %T would print the static type it always would print
>> interface{}.
>> To be useful Printf has too look inside it's arguments and inside is a
>> HelloInt.
>
>
> Mr. Dobler,
>
> Thank you for your reply!
>
> I agree with your statement that to be useful, the Printf function must do
> what it does. And, of course I want it to be useful :-)
>
> However, I am still concerned about this language from the spec:
>
> "The static type (or just type) of a variable is the type given in its
> declaration, the type provided in the new call or composite literal, or
the
> type of an element of a structured variable."
>
> Where it says "just type" means that anywhere the documentation uses the
> word "type" without qualification, it is referring to the static type. In
> the case of Printf, then, yes, %T should always print "interface{}"
because
> that is the variable's static type.
>
> I 200% (that's more than 100% :-)) agree with you that is not useful.
> However, based on the language in the spec, it is how I would expect it to
> operate.
>
> I sincerely appreciate your willingness to read through my message and
offer
> your reply. I am already learning very much!
I think you are being misled by trying to use the language in the spec
to interpret the meaning of %T in the fmt package. Perhaps the fmt
package docs should be updated, but the actual behavior is not going
to change. What %T prints is the type of the value passed in, unless
the value passed in has an interface type, in which case it prints the
dynamic type of the value.
Ian
Thank you so much for your reply. I definitely agree with you and do not
want the behavior to change at all. I just wanted the language to be
clarified. As I said in my last email, it seems like any change to the fmt
documentation would also need to be made to the reflect documentation. The
word "type" in both of those areas obviously and correctly refers to the
dynamic type which is in conflict with the definition of the (unqualified)
term type from the spec. Is there a place that I can advocate for such a
change?
Thanks again for your response!
Will
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