[plt-scheme] Need more class examples?

Thanks a lot!  , it's very clear now ,    thanks Carl and Ryan .


On Wed, Nov 19, 2008 at 12:40 AM, Ryan Culpepper <ryanc at ccs.neu.edu> wrote:
> On Nov 18, 2008, at 1:38 PM, Veer wrote:
>
>> Hello,
>>
>> This code :
>>
>> (define my-area% (class* object% (area<%>)
>>                  (init min-width)
>>                  (define mini-width min-width)
>>
>>                  (define/public (get-top-level-window)
>>                    this)
>>                  (define/public (get-parent)
>>                    #f)
>>                  (define/public (stretchable-height)
>>                    #f)
>>                  (define/public (stretchable-width)
>>                    #f)
>>                  (define/public (get-graphical-min-size)
>>                    0)
>>                  (define/public (min-width)
>>                    0)
>>                  (define/public (min-height)
>>                    0)
>>                  (super-new)))
>>
>> complains :
>> "class*: duplicate declared identifier in: min-width "
>>
>> My question is how you implement class method and init variable with same
>> name?
>> I tried to read the class reference manual , but its too complex for
>> me at the moment, so some examples
>> will be of great help.
>
>
> If you make it a (public) field, you can use the "renamed" version of the
> 'init-field' syntax:
>
>  (class* object% (area<%>)
>    (init-field ((mini-width min-width)))
>    ...)
>
> That declares two things:
>  - an initialization argument with an "external name" of 'min-width'
>  - a field named 'mini-width', whose initial value comes from the
> initialization argument
>
> If you don't want to make it a public field, then you can do this:
>
>  (class* object% (area<%>)
>    (init ((-min-width min-width)))
>    (define mini-width -min-width)
>    ...)
>
> Then you'd have three names instead of just two:
>  - 'min-width' is the external name of the initialization argument
>  - '-min-width' is the internal name of the initialization argument
>  - 'mini-width' is the name of the private instance variable
>
> Ryan
>
>
>
>>
>>
>> Thanks
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>
>