The SliceConstraint example also doesn't work.
Is the doc I mentioned outdated?
On Saturday, November 13, 2021 at 1:13:13 AM UTC+8 tapi...@gmail.com wrote:
> And this fails to compile, although the docs says it is valid:
>
> // sliceOrMap is a type constraint for a slice or a map.
> type sliceOrMap interface {
> []int | map[int]int
> }
>
> // Entry returns the i'th entry in a slice or the value of a map
> // at key i. This is valid as the result of the operator is always int.
> func Entry[T sliceOrMap](c T, i int) int {
> // This is either a slice index operation or a map key lookup.
> // Either way, the index and result types are type int.
> return c[i] // invalid operation: cannot index c (variable of type
> T constrained by sliceOrMap
> }
>
>
> On Saturday, November 13, 2021 at 1:10:30 AM UTC+8 tapi...@gmail.com
> wrote:
>
>> The proposal design docs (
>> https://go.googlesource.com/proposal/+/refs/heads/master/design/43651-type-parameters.md)
>>
>> mentions:
>>
>> // structField is a type constraint whose type set consists of some
>> // struct types that all have a field named x.
>> type structField interface {
>> struct { a int; x int } |
>> struct { b int; x float64 } |
>> struct { c int; x uint64 }
>> }
>>
>> // This function is INVALID.
>> func IncrementX[T structField](p *T) {
>> v := p.x // INVALID: type of p.x is not the same for all types in
>> set
>> v++
>> p.x = v
>> }
>>
>> However, it still fails to compile if all the types of the x fields are
>> identical.
>>
>> type structField interface {
>> struct { a int; x int } |
>> struct { b int; x int } |
>> struct { c int; x int }
>> }
>>
>> func IncrementX[T structField](p *T) {
>> v := p.x // p.x undefined (type *T has no field or method x)
>> v++
>> p.x = v // p.x undefined (type *T has no field or method x)
>> }
>>
>>
>>
>>
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