Well, that didn't go very far: https://go.dev/play/p/UtsrRar9J0Q
Fails with the messages
./prog.go:15:11: invalid operation: cannot index p_Map (variable of type
MAP constrained by DataMap)
./prog.go:16:26: cannot range over p_Map (variable of type MAP constrained
by DataMap) (MAP has no core type)
I think i have to to some more research here - or just copy and paste three
different typed functions…
Best regards from Charleston (WV),
Frank/2
Frank Jüdes schrieb am Mittwoch, 15. März 2023 um 05:51:10 UTC-4:
> Hi Kurtis,
> good to know that a map will always be "kind of" passed by reference to
> functions. I have verified that with a short test-program on the playground
> -> https://go.dev/play/p/HxdgpM-QozM
> So in the next code-review all those *[maptype] references will be
> removed. Things are very different in this case in other programming
> languages…
>
> I understand the misconception and that a map[type]interface{} won't
> automagically convert the data-type from the parameter into anything else.
> My intention was to explain the compiler to just accept whatever is fed
> into the function and just pass the data through to a function that uses
> interface{} for a single parameter. That's all this function needs to do:
> Accept a map of "something", get single values of "something" and pass them
> on to another function that accepts a single parameter of "something".
>
> I think i have found a solution in using a "generic" interface, stumbled
> upon this web-site:
> https://www.geeksforgeeks.org/generics-in-golang/?ref=rp
>
> And created a little test-program: https://go.dev/play/p/mOu1pmmfdX8
>
> This should allow me to pass different types of maps - actually i only
> need three types - to a generic function that passes the values on to
> another (generic) function.
>
> Thank you very much for your help.
>
> Best regards from Charleston (WV),
> Frank/2
>
> Kurtis Rader schrieb am Dienstag, 14. März 2023 um 22:57:13 UTC-4:
>
>> On Tue, Mar 14, 2023 at 7:07 PM Frank Jüdes <jue...@gmail.com> wrote:
>>
>>> Thank you very much Ian!
>>> I am using a pointer to the map because i want to pass the map by
>>> reference, not by value.
>>> Those maps can become pretty large and are being handed down through a
>>> couple of function calls and i don't want them to be copied over and over
>>> again.
>>>
>>
>> Maps are a special-case. You can't pass them "by value" in the sense you
>> mean because a "map" value is a very tiny structure that contains a pointer
>> to the actual map. Possibly the oldest public discussion of the fact maps
>> are reference type is this blog post: https://go.dev/blog/maps. Using a
>> pointer does, in fact, avoid copying that very small data structure but is
>> not necessary to keep from copying the entire map.
>>
>>
>>> I read the document you referenced, but am not able to understand…
>>> So i can use interface{} or any just to generalize simple types?
>>> Why is the compiler accepting then a p_Values map[string]interface{} as
>>> a parameter of a function? - What would be a compatible data-type to pass
>>> as this parameter?
>>>
>>
>> The compiler accepts a type of "map[string]interface{}" because that is
>> well defined and obviously useful, Functions, such as those in the fmt
>> package, would not be useful if a function could not deal with the
>> "interface{}" type directly or indirectly. Your confusion is very common
>> and arises from the misconception that the Go map implementation will
>> magically convert map values from a concrete type (e.g., "int") to the
>> "any" type if that is what is needed in a particular context. One reason it
>> doesn't do so is the same reason it doesn't auto-magically convert any
>> other map value type; e.g., "int" to "float".
>>
>> --
>> Kurtis Rader
>> Caretaker of the exceptional canines Junior and Hank
>>
>
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