Perhaps near the end of the type inference section, before "Note: type
inference is a convenience feature"? And perhaps something like this?
When discussing type inference, the term "type parameter" refers only to
the type parameters in a specific use of a generic function or type. For
example,
func Min[T interface{ type int, uint }](a, b T) T {
if b < a {
return b
}
return a
}
func Min3[U interface{ type int }](a, b, c U) U {
return Min(a, Min(b, c))
}
While inferring the type argument for the calls to Min, T is considered a
type parameter, but U is considered to be a fixed type, not subject to type
unification.
On Mon, Aug 24, 2020 at 4:47 PM Ian Lance Taylor <[email protected]> wrote:
> On Mon, Aug 24, 2020 at 4:34 PM Patrick Smith <[email protected]>
> wrote:
> >
> > I may be missing something, but it seems to me that one point in the
> draft's discussion of type inference could usefully be clarified (
> https://go.googlesource.com/proposal/+/refs/heads/master/design/go2draft-type-parameters.md#type-inference
> ).
> >
> > The term "type parameter" there should be restricted to the type
> parameters in the specific use of a generic type or function for which we
> are trying to infer type arguments. For example (
> https://go2goplay.golang.org/p/pWis3rlJElu)
> >
> > func Min[type T interface{ type int, uint }](a, b T) T {
> >
> > if b < a {
> >
> > return b
> >
> > }
> > return a
> >
> > }
> >
> > func Min3[type U interface{ type int }](a, b, c U) U {
> >
> > return Min(a, Min(b, c))
> >
> > }
> >
> > func BadMin3[type V interface{ type int, uint, string }](a, b, c V) V {
> >
> > return Min(a, Min(b, c))
> >
> > }
> >
> > Here, U and V are type parameters, but when inferring type arguments for
> the calls to Min, we must consider U and V as fixed types, not subject to
> type unification. This seems needed in order for the compiler to reject
> BadMin3.
>
> Thanks. That seems fairly clear to me, but I'm probably too close to
> the problem. Any suggestions for exactly where we should add a
> sentence, and what that sentence should be? Thanks.
>
> Ian
>
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