On Tue, Jan 22, 2019 at 11:47 PM <mountain...@gmail.com> 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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