RFR: 8264707: HotSpot Style Guide should permit use of lambda [v2]

[Kim Barrett]

On Thu, 23 Sep 2021 22:39:29 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
>> 
>>  - Merge branch 'master' into permit_lambda
>>  - terminology fix
>>  - add scope guard and some example uses
>>  - G1 SATB filter lambda
>>  - new local functions section
>
> src/hotspot/share/compiler/compilerOracle.cpp line 787:
> 
>> 785: 
>> 786:   char* original_line = os::strdup(line, mtInternal);
>> 787:   auto g = make_guard([&] { os::free(original_line); });
> 
> I have to admit that this usage is very mysterious.  I know you're going to take it out but using lambdas for something that's really hard to parse doesn't seem like a win.  Does save lines of code though.

I think a different approach may be possible, that would have usage like this:

char* original_line = os::strdup(line, mtInternal); 
ScopeGuard guard([&] { os::free(original_line); });

This would use something like (or maybe directly use) a solution to the type-erased lambda capturing problem a la std::function.

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PR: https://git.openjdk.java.net/jdk/pull/5144