Should you override #doesNotUnderstand: and #respondsTo: together?

> Question is, should X class>>canUnderstand: be overwritten, too?

This would not be possible in my example, would it? Each json object understands different keys ... This is also why I favor #respondsTo: over #canUnderstand: in general.

Best,

Christoph

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Von: Squeak-dev <[hidden email]> im Auftrag von Tobias Pape <[hidden email]>
Gesendet: Freitag, 31. Januar 2020 10:30:20
An: The general-purpose Squeak developers list
Betreff: Re: [squeak-dev] Should you override #doesNotUnderstand: and #respondsTo: together?

 

> On 31.01.2020, at 10:14, Thiede, Christoph <[hidden email]> wrote:
>
> Hi all,
>
> just struggled over the fact that Json objects provide access to their keys via #doesNotUnderstand:, but they do not override #respondsTo:. Example:
>
> json := Json readFromString: '{"foo": 42}'.
> json foo. "42"
> json respondsTo: #foo. "false"
>
> Question: Is this discrepancy indeed desired behavior? Or should we rather always try to override #doesNotUnderstand: and #respondsTo: together?

This is actually done very seldom, IIRC.
But maybe a good pattern, tho. Question is, should X class>>canUnderstand: be overwritten, too?

Best regards
        -Tobias

>
> Best,
> Christoph

When would you use this third boolean concretely? To me, this sounds rather like an overengineering solution, maybe premature optimization, for now ... :-)

Best,

Christoph

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Von: Squeak-dev <[hidden email]> im Auftrag von Jakob Reschke <[hidden email]>
Gesendet: Freitag, 31. Januar 2020 18:16:51
An: The general-purpose Squeak developers list
Betreff: Re: [squeak-dev] Should you override #doesNotUnderstand: and #respondsTo: together?

 

Regarding canUnderstand:, maybe it's time for the third boolean called "it depends" or "maybe". ;-)

Thiede, Christoph <[hidden email]> schrieb am Fr., 31. Jan. 2020, 10:43:

> Question is, should X class>>canUnderstand: be overwritten, too?

This would not be possible in my example, would it? Each json object understands different keys ... This is also why I favor #respondsTo: over #canUnderstand: in general.

Best,

Christoph

---

Von: Squeak-dev <[hidden email]> im Auftrag von Tobias Pape <[hidden email]>
Gesendet: Freitag, 31. Januar 2020 10:30:20
An: The general-purpose Squeak developers list
Betreff: Re: [squeak-dev] Should you override #doesNotUnderstand: and #respondsTo: together?

 

> On 31.01.2020, at 10:14, Thiede, Christoph <[hidden email]> wrote:
>
> Hi all,
>
> just struggled over the fact that Json objects provide access to their keys via #doesNotUnderstand:, but they do not override #respondsTo:. Example:
>
> json := Json readFromString: '{"foo": 42}'.
> json foo. "42"
> json respondsTo: #foo. "false"
>
> Question: Is this discrepancy indeed desired behavior? Or should we rather always try to override #doesNotUnderstand: and #respondsTo: together?

This is actually done very seldom, IIRC.
But maybe a good pattern, tho. Question is, should X class>>canUnderstand: be overwritten, too?

Best regards
        -Tobias

>
> Best,
> Christoph