Reflection on records

[Attila Kelemen]

I guess, if your record type is fixed, then you can have a dummy instance
of that record with all fields being different (hopefully, no 3 boolean
components :)), and then you can do the same hack as with the interface +
proxy combo.

Attila Kelemen <attila.kelemen85 at gmail.com> ezt írta (időpont: 2025. nov.
30., V, 20:51):

> I think that is impossible. What I did when I needed something similar is
> that I used an interface instead of a record and built utilities around it,
> because in that case you can imitate what you want.
>
> That is, consider that you have `interface User { String firstName();
> String lastName() }`. In this case, you could have methods taking a
> `Function<User, T>` and then you can create an instance of `User` via
> `Proxy.newProxyInstance` in which you record which method was called, and
> pass the proxy instance to the `Function`. Assuming that someone passed
> `User::firstName` for the `Function`, you can detect which method was
> passed. The drawbacks are obvious, but it is better than passing strings in
> my opinion.
>
> David Alayachew <davidalayachew at gmail.com> ezt írta (időpont: 2025. nov.
> 30., V, 20:41):
>
>> Thanks for the response Attila.
>>
>> Let me try and loosen the constraints then -- is there any way for me to
>> get a RecordComponent corresponding to firstName without needing to do
>> String comparison?
>>
>> At the end of the day, that's all that I really need.
>>
>> As is now, the only way I can see to get a RecordComponent is to drill
>> down from j.l.Class --> j.l.r.RecordComponent, then do String comparison
>> against a provided String to get the record component that I want. That is
>> unsafe and stringly typed, so, very much undesirable. After all, if I
>> change my record to say first instead of firstName, I want a compiler
>> error. But doing it that way, I won't -- I'll get a runtime error.
>>
>> So that's what I really want -- a type-safe way to isolate a record
>> component from a record, without forcing my users to have to provide a
>> String corresponding to the record component name.
>>
>> On Sun, Nov 30, 2025 at 2:16 PM Attila Kelemen <
>> attila.kelemen85 at gmail.com> wrote:
>>
>>> I'm pretty sure there is no such thing, because that essentially implies
>>> the existence of some kind of method literal (well, it would not be
>>> strictly necessary, but the JLS would feel strange without it), and there
>>> is no such thing (though it would be awesome, if there was).
>>>
>>> Also, note that if this was a thing, then your case is just a very
>>> special case, and you would want more (I would for sure). That is, in that
>>> case, I would also want type safety. So, something like
>>> MethodReference<(MyRecord) -> String> (which of course would require
>>> function types in Java).
>>>
>>> When I needed this, luckily I could restrain my need to interface
>>> methods (as opposed to your record getters) where I could create a `Proxy`
>>> and see which method gets called (nasty hack, has its downsides, but felt
>>> like the safest to me).
>>>
>>> Attila
>>>
>>> David Alayachew <davidalayachew at gmail.com> ezt írta (időpont: 2025.
>>> nov. 29., Szo, 20:50):
>>>
>>>> And by all means, add more parameters to foo if you want. For example,
>>>> if a User.class helps, please do so!
>>>>
>>>> I just don't want to do anything like this.
>>>>
>>>> foo("firstName");
>>>>
>>>> That's stringly typed, and undesirable for my use case.
>>>>
>>>
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