thanks lan.
在 2019年1月23日星期三 UTC+8下午11:26:57，Ian Lance Taylor写道：
>
> On Tue, Jan 22, 2019 at 11:47 PM <mount...@gmail.com <javascript:>>
> wrote:
> >
> > i got :
> > # command-line-arguments
> > ./key.go:6:18: invalid operation: F() == F() (func can only be compared
> to nil)
>
> Yes, that is what the language spec says and it is what I said: in Go,
> function values are not comparable.
>
> I wrote that code as an example to help explain why function values
> are not comparable.
>
> Ian
>
> > 在 2019年1月23日星期三 UTC+8上午11:59:07，mount...@gmail.com写道：
> >>
> >> When i use the func, map slice as the key of map, it isn't work!
> >> So I lookup source why, i find
> >>
> >> // spec: "The comparison operators == and != must be fully defined
> >> // for operands of the key type; thus the key type must not be
> a
> >> // function, map, or slice."
> >> //
> >> // Delay this check because it requires fully setup types;
> >> // it is safe to continue in any case (was issue 6667).
> >> check.later(func() {
> >> if !Comparable(typ.key) {
> >> check.errorf(e.Key.Pos(), "invalid map key type %s",
> typ.key)
> >> }
> >> })
> >> // Comparable reports whether values of type T are comparable.
> >> func Comparable(T Type) bool {
> >> switch t := T.Underlying().(type) {
> >> case *Basic:
> >> // assume invalid types to be comparable
> >> // to avoid follow-up errors
> >> return t.kind != UntypedNil
> >> case *Pointer, *Interface, *Chan:
> >> return true
> >> case *Struct:
> >> for _, f := range t.fields {
> >> if !Comparable(f.typ) {
> >> return false
> >> }
> >> }
> >> return true
> >> case *Array:
> >> return Comparable(t.elem)
> >> }
> >> return false
> >> }
> >
> > --
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