One of our go app crashed recently because of a bug in https://github.com/urfave/cli/, here is the PR with fix from my collegue who found the issue. Then we started talking about it internally and found something that’s interesting. I understand some of it but not fully so I thought of asking people who might know.
My question is why bar works but not foo.
package main
import (
"fmt"
)
func main() {
var f interface{}
var b interface{}
f = foo()
b = bar()
if _, ok := f.(func(string) error); ok {
fmt.Println("FOUND IT")
} else {
fmt.Println("DIDNT FIND IT")
}
if _, ok := b.(func(string) error); ok {
fmt.Println("FOUND IT")
} else {
fmt.Println("DIDNT FIND IT")
}
}
type FooFunc func(string) error
func foo() func(string) error {
return func(e string) error {
return fmt.Errorf("GOTCHA")
}
}
func bar() FooFunc {
return func(e string) error {
return fmt.Errorf("GOTCHA")
}
}