Re: [Cbor] CDDL Module Design

[Carsten Bormann <[e-mail]>]

> On 2020-07-01, at 23:40, Michael Richardson <[e-mail]> wrote:
> 
> 
> Michael Richardson <[e-mail]> wrote:
>>> On 2020-07-01, at 05:54, Michael Richardson <[e-mail]> wrote:
>>>> 
>>>> I prefer that the statement not be a pre-processor-like hack.
> 
>>> The C/C++ preprocessor may be considered a hack because it operates at
>>> a lexical level.  We should not make that mistake.  Apart from that, it
>>> does useful things.
> 
>>> Or, in other words, your hack may be my perfect layering.
> 
>> I agree.
>> As has been pointed out in
>> https://www.goodreads.com/book/show/44919.Working_Effectively_with_Legacy_Code
> 
>> the preprocessor is a really good tool for inserting shims.
> 
> The word I wanted was "seams", not shims.
> C gives you pre-processor seams, and link seams.
> Java lets you have neither.
> 
> A seam is a way to replace some function, usually something low-level like
> "open(2)" or "socket(2)" so that in a unit test you can feed in test data
> rather than live data.

We call that a “mock” (see [1] for another take of this, which involves “fake”s).  (Which may be implemented as a shim, i.e., recurring on the real function, which when made into an art form is also known as “advising” or “advice” [2].  Or as a “stub”.)

Real programming involves the use of linker scripts, where you often can rearrange some of the symbols or map one to the other.  I think it would be good if we have some isolation between the world of external names (and name references) and the internal symbols in a specification.  If this is not to become too tedious, some optional automation of setting up the mapping (and a way to gradually escape that automation) is desirable.

Hacking some of this functionality together at the lexical level (as the preprocessor makes you do) usually provides leaky abstractions, where the leak eventually bites you.  That’s why CDDL has generics, not macros (not that macros would be wrong, if done hygienically instead of lexically).

Grüße, Carsten

[1]: https://www.infoworld.com/article/3143104/my-two-cents-on-fakes-stubs-mocks-and-shims.html
[2]: https://en.wikipedia.org/wiki/Advice_(programming)