Ah, thanks, surprised I've never hit this issue before. So, for purely academic reasons, what if I wanted to write a function to look inside an interface value to determine if its value pointer is nil?
I tried this, following from your simplified example Steven.... https://play.golang.org/p/oG2aQzlKfc var m map[string]interface{} var i interface{} = m // i is interface{}, right? id := reflect.ValueOf(i).InterfaceData() // nope, panics "call of reflect.Value.InterfaceData on map Value" On Monday, 8 August 2016 19:05:53 UTC+1, Steven Blenkinsop wrote: > > Perhaps for clarity, the trip through reflect is a red herring. All you > need is to put the map in an interface: > > package main >> >> import ( >> "fmt" >> ) >> >> func main() { >> var m map[string]interface{} >> if m != nil { >> panic("m != nil") >> } >> var i interface{} = m >> if i == nil { >> // I expect this. >> fmt.Println("OK") >> } else { >> // This is what happens. >> fmt.Printf("nil != %# v\n", i) >> } >> // output: >> // nil != map[string]interface {}(nil) >> } >> > > The reason the interface is non-nil in this case is described in Ian's > link. > > On Mon, Aug 8, 2016 at 1:27 PM Ian Lance Taylor <ia...@golang.org > <javascript:>> wrote: > >> On Mon, Aug 8, 2016 at 10:07 AM, Sam Salisbury <samsal...@gmail.com >> <javascript:>> wrote: >> > The code speaks for itself, I thought I was understanding reflection up >> > until this point... It seems that the zero value of maps is nil, until >> you >> > round-trip them to a reflect.Value, and they become non-nil. >> >> This is an instance of https://golang.org/doc/faq#nil_error . >> >> Ian >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts...@googlegroups.com <javascript:>. >> For more options, visit https://groups.google.com/d/optout. >> > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
