JDK 10: General Availability

Re:JDK 10: General Availability by WHoWHo on Wednesday March 21, 2018 @05:38AM (#16636621)

From my experience in 20 years of Java, it prevents the reusage of local vars, which mostly is wrong.

   Person p = ....
   p = doSomething(p)
   ...
   p = doSomethingElse(p)

is hard to reason about when it should be

   Person p = ....
   ... lots of code
   Person updated = doSomething(p) 
   ... lots of code
   doSomethingElse(updated)

Which is easier to read and understand. So you might have had bugs that would have been prevented with final, but you didn't attribute to final.

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Re:JDK 10: General Availability by fauigerzigerk on Wednesday March 21, 2018 @06:57AM (#16636944)

I remember bugs that were caused by the exact opposite. If p is superceded by updated then it's not a good idea to have both hanging around in the local scope.

You shouldn't be able to doSomethingElse(p) when you actually mean to doSomethingElse(updated).

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Re:JDK 10: General Availability by Moter8 on Wednesday March 21, 2018 @09:25AM (#16637779)

So basically, what rust prohibits.

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Re:JDK 10: General Availability by fauigerzigerk on Wednesday March 21, 2018 @09:37AM (#16637860)

I don't know Rust very well at all, but I believe that Rust would only prohibit that if p and updated were referencing the same thing. If updated was a modified copy of p then I don't think Rust would help. But I could easily be wrong on that.

What would help is splitting the function up so that you don't have multiple named variables representing multiple versions of the same thing in the same scope:

   Person doSomethingAndDots() {
     Person p = doSomething(...)
     ...
     return p 
   }

   main() {
      doSomethingElse(doSomethingAndDots())
   }

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Re:JDK 10: General Availability by andrewaylett on Wednesday March 21, 2018 @10:28AM (#16638238)

If the transformation function consumes p, rather than taking a reference to it, Rust will stop you from using the variable again afterwards.

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Re:JDK 10: General Availability by anon3474422 on Wednesday March 21, 2018 @10:15AM (#16638135)

Rust explicitly allows shadowing, that way you can have it both ways. An immutable variable that can't be reassigned but you can still reuse names.

That is to ease the pain of unwrapping nested types and error-checking intermediate steps so you don't have to come up with new names for each intermediate.

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Re:JDK 10: General Availability by melling on Wednesday March 21, 2018 @10:05AM (#16638060)

I really like being able to declare immutable variables with ‘let’ in Swift. Java should add the immutable option too. Although, ‘val’ makes more sense considering Kotlin and Scala use it.

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