In my case, being a new go learner the following bit of code stumped me. I
am receiving a interface{} value and I am trying to figure out the best way
to print it. If the value supports the fmt.Stringer() interface then I want
to use that, otherwise i can do some other things. So I came up with this:
func printer(foo interface{}) string {
switch t := foo.(type) {
....
case fmt.Stringer:
return t.String()
...
}
But this crashes when foo is really a nil pointer to a type which does
support Stringer. The problem is that there is no way for me to actually
know foo is nil and avoid it. I can not compare foo to nil because foo is
an interface so foo==nil is false, and my type assertion is converting it
to an interface too so i can not compare that to nil either. Literally the
only way this code can work is to just catch the error and return the
string "nil". This is hugely confusing behavior especially for a new comer.
Apart for this it seems to me the natural way to implement this kind of
code - for example in python the code is natural, and I wanted to carry the
same general technique to go:
def printer(foo):
if isinstance(foo, Stringer):
return foo.String()
...
Thanks
Michael.
On Tuesday, June 5, 2012 at 8:50:00 AM UTC+10, jgoldbg wrote:
>
> I'm a bit stumped and wondering if I'm overlooking some way, besides
> reflection,
> to determine whether the data pointed at by an interface{} is actually a
> nil
> pointer:
>
> http://play.golang.org/p/Isoo0CcAvr
>
> Any ideas what I'm overlooking?
>
> jonathan
>
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