Reconstruction expression with explicit deconstuctor (REWED)

[David Alayachew]

Adding -comments

On Sat, Sep 23, 2023 at 10:54 AM Attila Kelemen <attila.kelemen85 at gmail.com>
wrote:

> Note: I think you would have a better chance, if you sent the email to
> "amber-spec-comments" than "observers", since the people who can actually
> make changes are more likely to read the "comments" list.
>
> That said, I don't really see the usefulness of such a syntax (and adding
> new syntax in itself is a detriment). That is, if I understood you
> correctly, then your example would replace this:
>
> ```
> Point p = ...;
> Point pp = new Point(p.x() + 2, 0);
> ```
>
> which is shorter and a lot more obvious. And if we were to go to more
> complicated things (many properties), then it doesn't help that much,
> because as far as I understand you, your proposal is still positional in
> its deconstruction pattern, and the positional nature is usually what is
> awkward in structures with many properties.
>
>
> Harrison Chikwe <nhcdeveloper at gmail.com> ezt írta (időpont: 2023. szept.
> 23., Szo, 12:01):
>
>> Hi,
>>
>> I think that it is very useful to have when working with immutable
>> objects.
>>
>> For the purposes of this mail, let's call the design described in the
>> ambro-doc[1]:
>> reconstruction expression with implicit deconstructor (aka REWID).
>>
>> Has it been considered to make the deconstructor pattern explicit in the
>> reconstruction
>> expression (aka REWED)?
>> Doing so may remove the requirement to make names more significant in the
>> language.
>>
>> For example, given the following:
>>
>> Point p = ...;
>> Point pp = p with(int x, int y) { x += 2; y = 0; }
>>
>> We can interpret the reconstruction expression above as:
>>
>> . Find a deconstructor and constructor pair that has a signature that
>> matches (int, int)
>> . Deconstruct the target with the deconstructor
>> . Execute the block on RHS
>> . Invoke the constructor with the result.
>>
>> If we split the reconstruction expression into three steps:
>>
>> 1. Extraction
>> 2. Transformation
>> 3. Construction
>>
>> In REWID users are required only to do step 2 (transformation) and the
>> system handles 1 and 3. Whereas in REWED users are required to do step 1
>> and 2
>> and the system handles just step 3.
>>
>> # Other forms of REWED
>>
>> 1. Explicit Named deconstructor pattern
>>
>>    Point pp = p with Point(int x, int y) {...}
>>
>> 2. Explicit Var deconstructor pattern
>>
>>    Point pp = p with var(int x, int y) {...}
>>
>> 3. Explicit Unnamed deconstructor pattern
>>
>>    Point pp = p with(int x, int y) {...}
>>
>>
>> We can extend form 1 to include factory pattern:
>>
>>    Point pp = p with Point.factory(int x, int y) {...}
>>
>>
>> # Advantages
>>
>> 1. No need to make names significant.
>> 2. Can be combined with other patterns (e.g. unnamed pattern, var pattern)
>>
>>    Point pp = p with(int x, _) { x = 0; }
>>
>>
>> Nyehamene.
>>
>
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