Ahhhh, thanks a lot for your help and sorry for trivial question.
To test the type assertion I should use following code:
printerImpl, ok := p.(*printer.Printer)
if !ok {
panic("wrong type")
}
(*printerImpl).Print("test")
I was trying to call the 'Print' func as *printerImpl.Print("test") not
(*printerImpl).Print("test").
Thanks again!
2016-11-03 14:51 GMT+01:00 David Crawshaw <craws...@golang.org>:
> The Lookup method is returning a pointer to the symbol (That way the
> program can modify the value of Impl through the plugin.)
>
> I believe you can write:
>
> printerImpl := *p.(*printer.Printer)
>
> On Thu, Nov 3, 2016 at 9:44 AM, Ian Lance Taylor <i...@golang.org> wrote:
> > [ +crawshaw ]
> >
> > On Thu, Nov 3, 2016 at 12:51 AM, Mateusz Dymiński <dymin...@gmail.com>
> wrote:
> >> Hi,
> >>
> >> I am trying to load dynamically implementation of particular interface.
> I've
> >> created the example in following repo:
> >> https://github.com/mateuszdyminski/go-plugin
> >>
> >> I have interface - let's call it Printer:
> >> package printer
> >>
> >> type Printer interface {
> >> Print(text string)
> >> }
> >>
> >>
> >> And implementation of this interface:
> >> package main
> >>
> >> import (
> >> "fmt"
> >>
> >> "github.com/mateuszdyminski/go-plugin/printer"
> >> )
> >>
> >> func main() {
> >> Impl.Print("test")
> >> }
> >>
> >> type PrinterImpl struct{}
> >>
> >> func (p PrinterImpl) Print(text string) {
> >> fmt.Printf("[PrinterImpl] %s\n", text)
> >> }
> >>
> >> var Impl printer.Printer = PrinterImpl{}
> >>
> >>
> >> Then I can build that implementation of Printer as following:
> >> go build -buildmode=plugin printer.go
> >>
> >>
> >> The last step is to load dynamically created library 'printer.so':
> >> package main
> >>
> >> import (
> >> "fmt"
> >> "plugin"
> >> "reflect"
> >>
> >> "github.com/mateuszdyminski/go-plugin/printer"
> >> )
> >>
> >> func main() {
> >> lib, err := plugin.Open("printer.so")
> >> if err != nil {
> >> panic(err)
> >> }
> >>
> >> p, err := lib.Lookup("Impl")
> >> if err != nil {
> >> panic(err)
> >> }
> >>
> >> printerImpl, ok := p.(printer.Printer)
> >> if !ok {
> >> fmt.Printf("wrong type: %+v \n", reflect.TypeOf(p))
> >> panic("wrong type")
> >> }
> >>
> >> printerImpl.Print("test")
> >> }
> >>
> >>
> >> But when I run it with 'go run main.go' I got following error:
> >> wrong type: *printer.Printer
> >> panic: wrong type
> >>
> >> goroutine 1 [running]:
> >> panic(0x50fda0, 0xc42000c2d0)
> >> /home/md/.gvm/gos/master/src/runtime/panic.go:531 +0x1cf
> >> main.main()
> >> /home/md/workspace/go/src/github.com/mateuszdyminski/go-
> plugin/main.go:25
> >> +0x231
> >> exit status 2
> >>
> >>
> >> The type of the 'Impl' taken from 'reflect' package is
> '*printer.Printer'.
> >> Is it possible to cast it to the printer.Printer and not to the pointer
> to
> >> the interface?
> >>
> >> Thanks for any help!
> >>
> >> --
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