html.NewTokenizer returns a pointer to a Tokenizer. So, you probably want
to embed a pointer:
type MyTokenizer struct {
*html.Tokenizer
}
func NewMyTokenizer(i io.Reader) *MyTokenizer {
z := html.NewTokenizer(i)
return &MyTokenizer{z}
}
If for some reason your want/need the Tokenizer value, you'll need to
dereference it before making it part of your MyTokenizer structure:
type MyTokenizer struct {
html.Tokenizer
}
func NewMyTokenizer(i io.Reader) *MyTokenizer {
z := html.NewTokenizer(i)
return &MyTokenizer{*z}
}
Jason
On Monday, January 1, 2018 at 11:14:14 PM UTC-5, Tong Sun wrote:
>
>
>
> On Mon, Jan 1, 2018 at 10:21 PM, Ian Lance Taylor <ia...@golang.org
> <javascript:>> wrote:
>
>> On Mon, Jan 1, 2018 at 6:46 PM, Tong Sun <sunto...@gmail.com
>> <javascript:>> wrote:
>> >
>> > I think I generally understand how embedding
>> > (https://golang.org/doc/effective_go.html#embedding) works in GO.
>> > However, when it comes to the following problem, I'm at lost again.
>> >
>> > I'm trying to extend the `html.Tokenizer` with new methods of my own:
>> >
>> > type MyTokenizer struct {
>> > html.Tokenizer
>> > }
>> >
>> >
>> > func NewMyTokenizer(i io.Reader) *MyTokenizer {
>> > z := html.NewTokenizer(i)
>> > return *MyTokenizer(z)
>> > return &MyTokenizer{z}
>> > }
>> >
>> >
>> >
>> > so code like
>> >
>> > z := html.NewTokenizer(body)
>> > ...
>> > func parseBody(z *html.Tokenizer) {
>> > tt := z.Next()
>> > ...
>> > testt := z.Token()
>> > ...
>> >
>> >
>> > can become:
>> >
>> > z := NewMyTokenizer(body)
>> > ...
>> > func (z *MyTokenizer) parseBody() {
>> > tt := z.Next()
>> > ...
>> >
>> > testt := z.Token()
>> > ...
>> >
>> >
>> >
>> >
>> > However, I'm really struggling to make it work as I was expected.
>> >
>> > Somebody help please, what's the proper way to extend a type with new
>> > methods of my own, while still able to access all existing methods?
>>
>> The best way to get help for this is to show us precisely what you
>> did, ideally in a small complete, stand-alone, example,
>
>
> The *small complete, stand-alone, example *has been provided in OP as
>
> https://github.com/suntong/lang/blob/master/lang/Go/src/xml/htmlParserTokens.go
>
> and tell us
>> what you expected to happen, and tell us precisely what happened
>> instead.
>
>
> *What expected to happen*: adding the following would work:
>
> type MyTokenizer struct {
> html.Tokenizer
> }
>
>
> func NewMyTokenizer(i io.Reader) *MyTokenizer {
> z := html.NewTokenizer(i)
> return *MyTokenizer(z)
> return &MyTokenizer{z}
> }
>
>
>> In this case I don't know what to suggest because you didn't
>> say what you expect and you didn't say what happened.
>>
>
> Can't make it work. The
>
> return *MyTokenizer(z)
> return &MyTokenizer{z}
>
> Are just the last two attempts that I make, apart from many other failed
> attempts that I've lost track of, but *neither compiles*.
>
> > Further more, how to extend the above even further? --
>> >
>> > - I plan to define an interface with a new method `WalkBody()`, in
>> which a
>> > "virtual" method of `VisitToken()` is used.
>> > - Then I plan to define two different type of MyTokenizer, with their
>> own
>> > `VisitToken()` methods, so the same `WalkBody()` method defined in
>> > MyTokenizer will behave differently for those two different types.
>> >
>> > How to architect above in Go?
>>
>> First, think in Go terms, don't think in terms like "virtual method"
>> that do not exist in Go.
>>
>> What you want is something like
>>
>> type TokenVisitor interface {
>> VisitToken()
>> }
>>
>> Then your WalkBody function will take a TokenVisitor, and your
>> different types will implement different VisitToken methods.
>>
>> (I see that you said WalkBody method, but you probably want a WalkBody
>> function instead.)
>>
>
> I did meant WalkBody method. See:
>
>
> https://github.com/suntong/lang/blob/master/lang/Go/src/xml/htmlParserTokens.go#L54
>
>
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