golang type conversion not working as (I) expected

golang type conversion not working as (I) expected

I'm using go-flags to parse command line options.
Per the go-flags docs: "... [if] either -h or --help was specified in the
command line arguments, a help message will be automatically printed.
Furthermore, the special error type ErrHelp is returned."
The method I'm calling is:
func (p *Parser) Parse() ([]string, error) {
I'm invoking this with a simple:
args, err := parser.Parse()
A snippet from the file that defines ErrHelp looks like this:
type ErrorType uint
const (
// Unknown or generic error
ErrUnknown ErrorType = iota
// Expected an argument but got none
ErrExpectedArgument
// ...
// The error contains the builtin help message
ErrHelp
// ...
)
// Error represents a parser error. The error returned from Parse is of this
// type. The error contains both a Type and Message.
type Error struct {
// The type of error
Type ErrorType
// The error message
Message string
}
// Get the errors error message.
func (e *Error) Error() string {
return e.Message
}
func newError(tp ErrorType, message string) *Error {
return &Error{
Type: tp,
Message: message,
}
}
So they have this custom "Error" type. And in the Parse() method above,
internally, the error is getting created with a block of code like this:
help.ShowHelp = func() error {
var b bytes.Buffer
p.WriteHelp(&b)
return newError(ErrHelp, b.String())
}
As you can see newError() returns "*Error" as it's type. But the anonymous
function just above returns type "error" - so those types must be
compatible.(?)
But now back to the original problem - I'm just trying to see if my "err"
is an "Error" and has member "Type" equal to ErrHelp. So I try this:
if err != nil && flags.Error(err).Type == flags.ErrHelp {
Or even just this:
fmt.Printf("test:", flags.Error(err))
And either way the compiler gives me:
main.go:37: cannot convert err (type error) to type flags.Error
But does not state why that conversion can't be done. Any ideas?
(I don't get how (*Error) successfully converts to "error" in the
anonymous function above, and I even more don't get why if that works then
I can't convert it back the other way... I must be missing something
really dumb here, but I'm not seeing what it is.)