Re: [go-nuts] how to write methods for a generic Matrix[float64 constrained by Addable]?

['Jakob Borg' via golang-nuts]

Two minor issues; you can’t declare func (m *Matrix[float64]) NanToZero() 
because we don’t have specialisation, it needs to be func (m *Matrix[T]) 
NanToZero(), and you can’t have complex as one of the possible types because 
it’s impossible to convert a complex to a float.

https://go.dev/play/p/QnWoKJ4bRcI

//jb

On 10 Sep 2023, at 01:31, Jason E. Aten <j.e.a...@gmail.com> wrote:

I made a playground if anyone wants to play with it and figure out how to test 
their ideas.

https://go.dev/play/p/h1nqHJAdVG8

On Sunday, September 10, 2023 at 12:24:54 AM UTC+1 Jason E. Aten wrote:
Like how, specifically?

func (m *Matrix[float64]) NanToZero() {
    for i := 0; i < m.Nrow; i++ {
        for j := 0; j < m.Ncol; j++ {
            v := m.At(i, j).(float64)
            if math.IsNaN(v) {
                m.Set(i, j, 0)
            }
        }
    }
}
gives
./slurp1.go:944:9: invalid operation: cannot use type assertion on type 
parameter value m.At(i, j) (value of type float64 constrained by Addable)

On Sunday, September 10, 2023 at 12:04:53 AM UTC+1 Dan Kortschak wrote:
On Sat, 2023-09-09 at 15:39 -0700, Jason E. Aten wrote:
> New to generics... how can I write a method for a Matrix[float64]
> that uses a math function that expects a float64?   I get:
>
> ./slurp1.go:936:18: cannot use m.At(i, j) (value of type float64
> constrained by Addable) as float64 value in argument to math.IsNaN
>
> Casting it to float64() does not change this error(!)
>
> here is the essentials:
>
> type Addable interface {
>     ~complex128 | ~complex64 | ~float64 | ~float32 |
>         ~byte | ~uint16 | ~uint32 | ~uint64 |
>         ~int8 | ~int16 | ~int32 | ~int64 | ~int
> }
>
> type Matrix[T Addable] struct {
>     Nrow int
>     Ncol int
>     Dat        []T
> }
> ...
> func (m *Matrix[float64]) NanToZero() {
>     for i := 0; i < m.Nrow; i++ {
>         for j := 0; j < m.Ncol; j++ {
>
>             if math.IsNaN(m.At(i, j)) {  // line 936, where the error
> is; ./slurp1.go:936:18: cannot use m.At(i, j) (value of type float64
> constrained by Addable) as float64 value in argument to math.IsNaN
>
>                 m.Set(i, j, 0)
>             }
>         }
>     }
> }
>
> go version go1.20.6 linux/amd64

You will probably need to type assert.


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