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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: 0.209s | source
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jjmarr ◴[31 Mar 25 20:06 UTC] No.43539277[source]▶
From my perspective as a C++ developer, every attempt to use `const` for compiler optimization appears to be stymied by the existence of `const_cast`, because modifying a `const` value is only undefined behaviour if the underlying object is `const`. Glad to see that Java is willing to break the language to improve it.
replies(2): >>43539753 #>>43540159 #
PhilipRoman ◴[31 Mar 25 21:25 UTC] No.43540159[source]▶
The implementation of "const" in C/C++ is really annoying, in the end all you get is a bit of semantic documentation and a bunch of compiler errors or casts whenever some library doesn't use it. You can often trick the compiler into stronger optimizations by making a local variable marked as "const" (in which case it is a "true const") and copying the value to/from it.
replies(1): >>43552808 #
1. int_19h ◴[02 Apr 25 01:03 UTC] No.43552808[source]▶
The real problem is that "const" in C/C++ is a misnomer - the literal meaning of the word means "unchanging", and yet if you have a pointer or reference to a const T, it can, in fact, change. A "const pointer" in C is really a read-only pointer to some data that may or may not be actually constant.

In C, at least, you can usually distinguish a true pointer to immutable data by using `restrict`.