From 0fbae8050b6f853053c7dee6a43d3ffbcfa69954 Mon Sep 17 00:00:00 2001 From: Kim Barrett Date: Tue, 16 Sep 2025 04:42:50 +0000 Subject: [PATCH] 8252582: HotSpot Style Guide should permit variable templates Reviewed-by: dholmes, stefank, kvn --- doc/hotspot-style.html | 45 +++++++++++++++++++++++------------------- doc/hotspot-style.md | 33 +++++++++++++++++-------------- 2 files changed, 43 insertions(+), 35 deletions(-) diff --git a/doc/hotspot-style.html b/doc/hotspot-style.html index fb4cffc9d43..7be6867b3ca 100644 --- a/doc/hotspot-style.html +++ b/doc/hotspot-style.html @@ -86,8 +86,9 @@ values
  • thread_local
  • nullptr
  • <atomic>
    • -
  • Inline -Variables
    • +
  • Variable Templates and +Inline Variables
  • Initializing variables with static storage duration
    • @@ -937,12 +938,18 @@ differ from what the Java compilers implement.

    "conservative" memory ordering, which may differ from (may be stronger than) sequentially consistent. There are algorithms in HotSpot that are believed to rely on that ordering.

    -

    Inline Variables

    -

    Variables with static storage duration may be declared -inline (p0386r2). -This has similar effects as for declaring a function inline: it can be -defined, identically, in multiple translation units, must be defined in -every translation unit in which it is Variable Templates and +Inline Variables +

    The use of variable templates (including static data member +templates) (N3651) is permitted. +They provide parameterized variables and constants in a simple and +direct form, instead of requiring the use of various workarounds.

    +

    Variables with static storage duration and variable templates may be +declared inline (p0386r2), and this usage is +permitted. This has similar effects as for declaring a function inline: +it can be defined, identically, in multiple translation units, must be +defined in every translation unit in which it is ODR used, and the behavior of the program is as if there is exactly one variable.

    @@ -955,16 +962,17 @@ initializations can make initialization order problems worse. The few ordering constraints that exist for non-inline variables don't apply, as there isn't a single program-designated translation unit containing the definition.

    -

    A constexpr static data member is implicitly -inline. As a consequence, an A constexpr static data member or static data member +template is implicitly inline. As a consequence, an ODR use of such a variable doesn't -require a definition in some .cpp file. (This is a change from -pre-C++17. Beginning with C++17, such a definition is considered a -duplicate definition, and is deprecated.)

    -

    Declaring a thread_local variable inline is -forbidden for HotSpot code. The use of -thread_local is already heavily restricted.

    +title="One Definition Rule">ODR use of such a member doesn't require +a definition in some .cpp file. (This is a change from pre-C++17. +Beginning with C++17, such a definition is considered a duplicate +definition, and is deprecated.)

    +

    Declaring a thread_local variable template or +inline variable is forbidden in HotSpot code. The use of thread_local is already +heavily restricted.

    Initializing variables with static storage duration

    @@ -1853,9 +1861,6 @@ Features