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A comment on Two Weeks of Rust. Parent comment

Re:Two Weeks of Rust by markque on Tuesday January 12, 2016 @06:55AM (#10886869)
A somewhat contrived example which may require a quick look at the API docs but in the main you can focus on solving the problem, premature optimization and all that.
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Re:Two Weeks of Rust by jasode on Tuesday January 12, 2016 @07:16AM (#10886938)
> may require a quick look at the API docs

But that tradeoff of memory footprint vs performance implemented by Oracle is not in the API documentation[1] for Java 7 nor Java 8.

One would have to stumble across other sources such as unofficial blogs[2] written by non-Oracle employees like Mikhail Vorontsov. That blog article then triggers an explanation from the actual coder that's buried in a reddit thread[3].

Hunting down why your business-domain java code is now suddenly slower because of hidden GC tuning is taking time away from "solving the problem."

Your rebuttal consists of:

-- repeating the "premature optimization" meme which is not relevant in this case.

-- recommending to look at the API docs, which doesn't even have the information!

[1]v7: https://docs.oracle.com/javase/7/docs/api/java/lang/String.h...

v8: https://docs.oracle.com/javase/8/docs/api/java/lang/String.h...

[2]http://java-performance.info/changes-to-string-java-1-7-0_06...

[3]https://www.reddit.com/comments/1qw73v

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Re:Two Weeks of Rust by anon1385 on Tuesday January 12, 2016 @07:26AM (#10886977)
>A somewhat contrived example

It's not a contrived example. When Java changed this exact behaviour it caused a lot of pain for people. Code that previously ran in a reasonable amount of time suddenly became impractically slow:

https://news.ycombinator.com/item?id=9862556

>may require a quick look at the API docs

The behaviour isn't specified by the spec. That is why they were able to change it from one release to the next.

>premature optimization and all that.

The "premature optimization" meme you are parroting contains the implication that at some point optimisation will be necessary. When that happens you have to think about memory management, even in a GC language. The string example given by danieldk is just one of many ways in which that can happen.

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Re:Two Weeks of Rust by rakoo on Tuesday January 12, 2016 @09:24AM (#10887532)
> The "premature optimization" meme you are parroting contains the implication that at some point optimisation will be necessary. When that happens you have to think about memory management, even in a GC language. The string example given by danieldk is just one of many ways in which that can happen.

That's exactly the point: caring about the actual memory used by interesting may not be as important as other parts of the application, or may not be important at all for now. You should only care about that when it does prevent pose a problem (performance, impossibility to evolve features, ...) (all while making the initial code flexible enough to be potentially changed in the future)

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Re:Two Weeks of Rust by danieldk on Tuesday January 12, 2016 @09:51AM (#10887694)
You should only care about that when it does prevent pose a problem

Then you are setting up yourself for a lot of trouble.

Another part of memory management is thinking about ownership (to which the substring discussion is very much related) and it pains me to see how many bugs are caused by code like:

   Foo getFoo() {
     return myFoo;
   }
Where Foo is some mutable class and the invariants of the wrapping class suddenly don't hold anymore because some outside code is mutating the Foo instance through the pointer/reference.

Throw in some amount of concurrency and you get something that is not only hard to debug but also difficult to reproduce.

tl;dr: in a GCed language you need to think about memory management and ownership as well.

(Note: I am not arguing against garbage collection.)

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Re:Two Weeks of Rust by wtetzner on Tuesday January 12, 2016 @12:53PM (#10888988)
> Where Foo is some mutable class

Ah, there's your problem :)

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Re:Two Weeks of Rust by jerf on Tuesday January 12, 2016 @09:00AM (#10887403)
I'm firmly of the opinion that GC is the correct default [1] and that removing GC ought to be considered an optimization, not a default choice, but there's nothing contrived about that example. I've written apps where I had to know what was going on.

[1]: At least between GC and not-GC. Rust is a new third option IMHO.

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