4 ms·

If I understand this correctly then Integer becomes a value class and every instance of it loses its object identity. I do not have a lot of knowledge about th

If I understand this correctly then Integer becomes a value class and every instance of it loses its object identity. I do not have a lot of knowledge about the details but from the outset it seems like a rather bold move to me.

agilob 3mo ago
Java has a mechanism for Integer and Long objects caching using something that already looks like value object, cached objects can be compared using ==. hashCode of Integer already returns int, the boxed int value. Not much of value is lost.
- swiftcoder 3mo ago
  Of particular note, all 1-byte Integers are interned, there is a pool of small Integers from -127 <-> 127 which are reused whenever possible. I learned this the hard way, when a C++ JNI extension I was working on accidentally overwrote the pooled value for zero, and all hell broke loose...
  - agilob 3mo ago
    > Integers from -127 <-> 127 The cache can be extended on startup with env var `java.lang.Integer.IntegerCache.high ` https://github.com/openjdk/jdk/blob/cc278dbb8a1ca0754d5842708b9029441055d361/src/java.base/share/classes/java/lang/Integer.java#L927 https://github.com/openjdk/jdk/blob/cc278dbb8a1ca0754d584270...
    - pwagland 3mo ago
      That is a nice piece piece of knowledge! We have an Integer cache in our product, and the only reason that it hangs around is that it caches 0..1024 instead of -127..128. By setting this value, we could simplify our code, ever so slightly.
  - tpm 3mo ago
    Yeah - it's a bit non-intuitive you can change the value of a number. https://thedailywtf.com/articles/Disgruntled-Bomb-Java-Edition https://thedailywtf.com/articles/Disgruntled-Bomb-Java-Editi...
    - inigyou 3mo ago
      In Python 2 you could literally do True = False and of course in JavaScript undefined = "a string"
      - swiftcoder 3mo ago
        The terrifying part of this in Java, is that it applies program-wide, including to constants set before you changed the value
    - J-Kuhn 3mo ago
      Such hacks will slowly stop working (without explicitly allowing it from the command line.) In this example, it would throw an IllegalAccessException, because java.base doesn't open java.lang.
      - vips7L 3mo ago
        Doesn’t field.setAccessible(true) already throw on a modern version?
        J-Kuhn 3mo ago
        Exactly. You can make it not throw by adding `--add-opens java.base/java.lang=ALL-UNNAMED` or similar to the command line, but breaking things like this is becoming harder.
  - deleted 3mo ago
    [deleted]
josefx 3mo ago
Any project depending on Integer identity had years of warning that this change would come. Also given implicit primitive conversions and object pooling Integer isn't exaclty a prime candidate for object identity to begin with.
ivolimmen 3mo ago
As far as I understood this (plus future work) will make value classes work more like structs meaning it will save memory and align memory better for things like gRPC, etc.
titzer 3mo ago
Wait, what? Virgil targeting the JVM does rely on that to represent vacuous arrays like `Array<void>`. That's annoying.

agilob 3mo ago

Java has a mechanism for Integer and Long objects caching using something that already looks like value object, cached objects can be compared using ==. hashCode of Integer already returns int, the boxed int value. Not much of value is lost.

swiftcoder 3mo ago
Of particular note, all 1-byte Integers are interned, there is a pool of small Integers from -127 <-> 127 which are reused whenever possible. I learned this the hard way, when a C++ JNI extension I was working on accidentally overwrote the pooled value for zero, and all hell broke loose...
- agilob 3mo ago
  > Integers from -127 <-> 127 The cache can be extended on startup with env var `java.lang.Integer.IntegerCache.high ` https://github.com/openjdk/jdk/blob/cc278dbb8a1ca0754d5842708b9029441055d361/src/java.base/share/classes/java/lang/Integer.java#L927 https://github.com/openjdk/jdk/blob/cc278dbb8a1ca0754d584270...
  - pwagland 3mo ago
    That is a nice piece piece of knowledge! We have an Integer cache in our product, and the only reason that it hangs around is that it caches 0..1024 instead of -127..128. By setting this value, we could simplify our code, ever so slightly.
- tpm 3mo ago
  Yeah - it's a bit non-intuitive you can change the value of a number. https://thedailywtf.com/articles/Disgruntled-Bomb-Java-Edition https://thedailywtf.com/articles/Disgruntled-Bomb-Java-Editi...
  - inigyou 3mo ago
    In Python 2 you could literally do True = False and of course in JavaScript undefined = "a string"
    - swiftcoder 3mo ago
      The terrifying part of this in Java, is that it applies program-wide, including to constants set before you changed the value
  - J-Kuhn 3mo ago
    Such hacks will slowly stop working (without explicitly allowing it from the command line.) In this example, it would throw an IllegalAccessException, because java.base doesn't open java.lang.
    - vips7L 3mo ago
      Doesn’t field.setAccessible(true) already throw on a modern version?
      - J-Kuhn 3mo ago
        Exactly. You can make it not throw by adding `--add-opens java.base/java.lang=ALL-UNNAMED` or similar to the command line, but breaking things like this is becoming harder.
- deleted 3mo ago
  [deleted]

josefx 3mo ago

Any project depending on Integer identity had years of warning that this change would come. Also given implicit primitive conversions and object pooling Integer isn't exaclty a prime candidate for object identity to begin with.

ivolimmen 3mo ago

As far as I understood this (plus future work) will make value classes work more like structs meaning it will save memory and align memory better for things like gRPC, etc.

titzer 3mo ago

Wait, what? Virgil targeting the JVM does rely on that to represent vacuous arrays like `Array<void>`. That's annoying.