[go-nuts] About struct fields in type parameters

[tapi...@gmail.com]

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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