Reconstruction expression with explicit deconstuctor (REWED)

[David Alayachew]

Also adding @amber-dev <amber-dev at openjdk.org>

On Wed, Oct 18, 2023 at 8:00 PM David Alayachew <davidalayachew at gmail.com>
wrote:

> 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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