...I have not been able to find it meaningful elsewhere.
sorry, i forgot,
- ultimately, type D struct {r<t:Interface>}, does not make sense either
imo.
On Thursday, July 20, 2017 at 6:21:21 AM UTC+2, [email protected] wrote:
>
> I think your example is not relevant, as it clearly intend to change the
> input type,
> the goal is to preserve it, while still working with its value.
>
>
> interface{} value type destroys the input type information,
> so you might have the opposite value type,
> a type that preserves.
> A type that let you write, *func, please, return the type i got*.
>
> I did not mention templating, code generate / whatever/ like in
> https://en.wikipedia.org/wiki/Generic_programming
>
> I read something related in "*Generic programming* is a style of computer
> programming <https://en.wikipedia.org/wiki/Computer_programming> in which
> algorithms <https://en.wikipedia.org/wiki/Algorithm> are written in terms
> of types <https://en.wikipedia.org/wiki/Data_type> *to-be-specified-later*
> that are then *instantiated* when needed for specific types provided as
> parameters
> <https://en.wikipedia.org/wiki/Parameter_%28computer_programming%29>."
>
> ...*to-be-specified-later... *runtime leaks in the static type system,
> mostly a question of pov.
>
> - <t> behaves like interface{} value type, because it does still say
> absolutely nothing. Not because it lacks of identity, but because it
> represents too many possible type.
> - <t:Interface> is a shorthand to avoid a, probably, very repetitive type
> assert in order to use a <t>, much like an interface{}, but better, because
> its shorter
> - <t> can be use only in func/method parameter (*excluded *receiver) ? I
> have not been able to find it meaningful elsewhere.
> - if you don t need to return the input type, you don t need <t>
> - ultimately, []interface{} == []<t>, they both are list of stuff we have
> no idea what its about, but <t> has no sense if it is not scoped to a
> function call stack.
> - ultimately, []<t:Stringer> does not make sense.
>
> - when you receive a func (x <t>) <t> {}, it does actually says nothing to
> you, the declarer of the func, not because it lacks of identity, but
> because it represents too many possible types. If you d want to do
> something of it, you need to type assert it, to narrow it to something
> meaningful.
> - when you receive a constrained <t:Interface>, you can work on value of
> type Interface, and you can return whatever, including the input parameter
> type
> - when you call a func with a constrained type, you can actually
> statically verify that the input value satisfies the constraint.
> - when you call a <t>, anything is as good as nil (i guess)
>
>
>
> On Wednesday, July 19, 2017 at 11:47:40 PM UTC+2, Eric Johnson wrote:
>>
>> While I lean towards the view that Go should add support for type
>> generics, I'm not sure your example actually provides sufficient detail to
>> be an argument for them.
>>
>> On Monday, July 17, 2017 at 2:07:46 AM UTC-7, [email protected] wrote:
>>>
>>> in func do(i interface{}) interface{} (return i), do says nothing
>>> because "interface{} says nothing",
>>>
>>> from the caller pov, it looses information at the return call,
>>>
>>> var x = "o"
>>> do(x) // <- return lost the track it was a string
>>>
>>> if you delegate that func to another func,
>>> it can t says anything else rather than nothing unless it introduces
>>> type assertion.
>>> func to(do func(interface{})interface{}) func (interface{}) interface{}
>>> { return func (i interface{}) interface{} {return do(i)} }
>>>
>>> if the observation become "interface{} destroys information",
>>> does it make sense to consider a "value type of any type that carries
>>> out its input type" ?
>>> func do(any <t>) <t> {return any}
>>> do("thing") <- this is explicitly string
>>>
>>> Acting the same way as interface, except that little thing about
>>> destroying/preserving an information.
>>>
>>> It can be delegated to func that works on anything, still returns
>>> concrete types.
>>> func to(do func(*<t>*)<t>) func (<t>) *<t>* { return func (i <t>) <t>
>>> {return do(i)} }
>>>
>>> to(do)("whatever") // got a string, right ?
>>>
>>> One step forward,
>>> what if <t> might be able to say "any type with a constraint on that
>>> interface",
>>> func do(any <t:Stringer>) <t> {return any}
>>> do(WhateverStringerCapable{}) <- much like using a regular parameter of
>>> type Stringer/interface{}, but now the return call reflects the invoke call
>>> , so its more complete than interface{}/Stringer.
>>>
>>
>> If the "do" method takes and returns a Stringer, then why not just
>> declare it that way? To make this a more interesting discussion, you have
>> to get into the details of what the "do" function actually needs to do? Why
>> can't it just use standard interfaces?
>>
>> As I see it, one of the generics problems comes from using the built-in
>> slices and maps. As it current stands, if I create a method:
>>
>> func concat(foo []Stringer) String {
>> result = ""
>> for _, s := range foo {
>> result = result + s.String() + ";
>> }
>> return result
>> }
>>
>> but suppose I have two structs, Foo, and Bar, and both *Foo, and *Bar
>> implement Stringer.
>>
>> I cannot do this:
>> func myFunc(f []*Foo, b []*Bar) string {
>> return concat(f) + concat(b)
>> }
>>
>> This seems like a more concrete scenario than the one you identified.
>>
>> Eric.
>>
>>
>>>
>>> no?
>>>
>>> Or maybe there is a reason in destroying that information ?
>>>
>>
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