Re: [PATCHv2 1/2] hashmap.h: compare function has access to a data field

> Stefan Beller <sbeller@google.com> writes:
>
>> Ok, let me redo the patch to have fndata at the front.
>>
>> Looking at other places (that have a similar mechanism mechanically,
>> but are semantically different), such as the callback functions for
>> the diff machinery, we have the user provided pointer at the end
>> of the list. But that is because the diff_options are the objects that
>> should be in front row (they are bound to the callback more than
>> some caller needed data).
>
> Quite honestly, I do not care too deeply about an API specific to a
> particular area like "diff" that passes its "configuration" data
> that everybody in the API knows, i.e. diff_options.  If the
> convention for ordinary functions in the API is to pass that in a
> particular location in the parameter list, I would think it is good
> for a application-supplied callback function to follow that pattern.
> After all, it is to configure the behaviour of the "diff" and the
> caller-supplied callback could have been part of a (hypothetically
> richer) API implementation.
>
> But I view a comparison function that is given to hashmap that is
> supplied by the caller a bit differently.  It is not about
> "hashing", so the reason to have the data close to function pointer
> is stronger there.