On Fri, May 3, 2019 at 7:57 AM Louki Sumirniy
<louki.sumirniy.stal...@gmail.com> wrote:
>
> Ellipsis makes the parameter type into a slice, but in append it makes the
> append repeat for each element, or do I misunderstand this?
>
> There is a syntactic distinction between them too. Parameters it is a prefix
> to the type, append it is a suffix to the name. It neatly alludes to the
> direction in which the affected variable is operated on - inside the function
> name ...type means name []type and for append, we are splitting the slice
> into a tuple (internally), at least as I understand it, and the parameter is
> the opposite, tuple to slice.
>
> I sometimes lament the lack of a tuple type in Go (I previously worked a lot
> with Python and PHP), but []interface{} isn't that much more difficult and
> the ellipsis syntax is quite handy for these cases - usually loading or
> otherwise modifying essentially a super simple container array.
For any function F and some type T declared as
func F(x ...T) {}
within F x will have type []T. You can call F with a slice s of type []T as
F(s...)
That will pass the slice s to F as the final parameter. This works
for any variadic function F.
The append function is implicitly declared as
func append(to []byte, add ...byte)
You can call it as
append(to, add...)
Here F is append and T is byte.
There is a special case for append with an argument of type string,
but other than that append is just like any other variadic function.
Ian
> On Friday, 3 May 2019 16:44:47 UTC+2, Ian Lance Taylor wrote:
>>
>> On Fri, May 3, 2019 at 7:34 AM Louki Sumirniy
>> <louki.sumi...@gmail.com> wrote:
>> >
>> > The ellipsis has two uses in Go, one is in variadic parameters, the other
>> > is in the slice append operator. It is essentially an iterator that takes
>> > a list and turns it into a slice (parameters) or takes a slice and turns
>> > it into a recursive iteration (append). Parameters with the ellipsis are
>> > addressed inside the function as a slice of the type after the ellipsis.
>>
>> Note that there is nothing special about append here, it's just like
>> passing a slice to any other variadic parameter. See
>> https://golang.org/ref/spec#Passing_arguments_to_..._parameters .
>>
>> Ian
>
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