Bingo! Thanks a lot for your *clear explanation* Jason! I went with your
first choice and it works perfectly.
Now wish somebody can answer the second part -- extend it even further for
two different `VisitToken()` behaviors...
On Mon, Jan 1, 2018 at 11:39 PM, Jason Phillips <jasonryanphill...@gmail.com
> wrote:
> 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>
>> wrote:
>>
>> On Mon, Jan 1, 2018 at 6:46 PM, Tong Sun <sunto...@gmail.com> 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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