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JEP draft: Prepare to make final mean final

(openjdk.org)
204 points mfiguiere | 1 comments | 31 Mar 25 19:35 UTC | HN request time: 0.21s | source
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stickfigure ◴[31 Mar 25 20:06 UTC] No.43539275[source]▶
Great! Now can we make `final` the default for all fields, variables, and parameters?

(yes yes, I know, that would break syntax... but please come up with something to discourage mutability)

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magicalhippo ◴[31 Mar 25 20:10 UTC] No.43539333[source]▶
Const-ness in C++ is something I miss in other languages. Being immediate able to see that this function or method couldn't mutate the object made it so much easier to reason about the code.

Yeah I know there's ways around it, but then the author known what they told the other party to expect.

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josephg ◴[31 Mar 25 20:29 UTC] No.43539580[source]▶
Yeah I find it a bit startling going from rust (where const is the default) to basically any other language. Sometimes I look at typescript function definitions and I’m like - uuuuhhh does this function mutate that parameter? Does it keep a reference to it? If the object I’m passing is mutated after I call this function, will something break? It’s impossible to tell from a function signature, even with all of typescript’s type safety. That gives me the willies. - and for good reason, it’s tripped me up lots of times.

Even the JS standard library struggles with this. You just have to remember that .sort() modifies the array in place (and returns it), but .slice() does a shallow clone of the array. (Not a deep clone - that would be different again!)

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mont_tag ◴[31 Mar 25 20:45 UTC] No.43539769[source]▶
> Even the JS standard library struggles with this. You just have to remember that .sort() modifies the array in place

ISTM that there are almost always some kinds of mutable data structures present in non-trivial programs. And outside of the program, you have databases to directories of files that get mutated by users or other parts of a program. I think this is just a fact of life.

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1. magicalhippo ◴[31 Mar 25 20:54 UTC] No.43539870[source]▶
The point isn't that there's mutability, it's to be able to easily identify where it is and where it is not.

Languages which lack the tools to do this are just harder to reason about, at least for me.

In the JS example, as a non-JS coder, I would expect that a sort function that returns nothing/void would sort in-place, while a sort function that returns an array would return a sorted copy. I would not expect it to sort in-place and return it.

However in C++ I could easily see from the function definition that it might be doing that, because a sort that returns a copy would take a const reference for the input array. So if I came across a sort function which took a non-const reference as input I'd be able to at least suspect it's doing it in-place.