Hello Ian.
Here's a complete example constructed from the snippets:
-------------------------
package main
type Fun func()
type Alpha struct {
}
func (a Alpha) funA() {
}
type Beta struct {
}
func (b Beta) funB() {
}
var a1,a2,a3,a4,a5 Alpha
var b1,b2,b3,b4,b5 Beta
var f Fun
func main() {
f = a1.funA
f = b1.funB
// Challenge: construct an expression that evaluates to true only if f
is assigned to `funA` of any instance of `Alpha`
}
-------------------------
https://play.golang.org/p/HoGGR0NeLE2
Thanks!
Kind regards,
Howard
On Tue, 11 Jun 2019 at 01:10, Ian Lance Taylor <i...@golang.org> wrote:
>
> On Sun, Jun 9, 2019 at 10:17 PM Houzuo Guo <guohou...@gmail.com> wrote:
> >
> > Thanks very much Ian - indeed I should have proof read the message. With
> > the last paragraph, I wished to ask for a way to tell a non-nil ` var f
> > Fun` is assigned to `funA` of any instance of structure Alpha, or `funB` of
> > any instance of structure Beta - without performing equality comparison
> > between the instances' method and the `f` variable.
> >
> > Take an example - suppose there are:
> > - var a1,a2,a3,a4,a5 Alpha
> > - var b1,b2,b3,b4,b5 Beta
> > - var f Fun
> >
> > And that `f` is assigned to any of:
> > - a1.funA, a2.funA ...
> > - b1.funB, b2.funB ...
> >
> > Without performing equality check (f == a1.funA || f == a2.funA || f ==
> > a3.funA ...), construct a test condition that evaluates to true only if `f`
> > is assigned to `funA` of any instance of `Alpha`.
>
> But in your code funA and funB are methods. You can't assign f to
> a1.funA. You can't change a1.funA at all.
>
> Can you show a small runnable example of what you are asking about?
>
> Ian
>
>
>
>
> > On Monday, 10 June 2019 07:46:58 UTC+3, Ian Lance Taylor wrote:
> >>
> >> On Sun, Jun 9, 2019 at 9:48 AM Houzuo Guo <guoh...@gmail.com> wrote:
> >> >
> >> > Given a function type: type Fun func()
> >> >
> >> > And two structure methods that satisfy the function type:
> >> >
> >> > type Alpha struct {
> >> > }
> >> > func (a Alpha) funA() {
> >> > }
> >> >
> >> > type Beta struct {
> >> > }
> >> > func (b Beta) funB() {
> >> > }
> >> >
> >> > At runtime, is there a way to tell whether a non-nil `var f Fun` is
> >> > assigned to an arbitrary instance of structure Alpha, or Beta? Can
> >> > reflection help in this case?
> >>
> >> I'm sorry, I don't understand your question. funA and funB are
> >> methods. You can't assign to a method. And the structs have no
> >> fields, so you can't assign to that either. So I'm not sure what you
> >> mean.
> >>
> >> That said, I suspect the answer to your real question is "no."
> >>
> >> Ian
> >
> > --
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