Give basic_memory_buffer allocator [[no_unique_address]] #3485
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Following the advice from https://devblogs.microsoft.com/cppblog/msvc-cpp20-and-the-std-cpp20-switch/ on how to use [[msvc::no_unique_address]]. Attempting to use it in standards prior to C++20 works, but emits a warning, so I opted to only enable this when FMT_CPLUSPLUS >= 202002L. Alternatively, a pragma warning disable for MSVC can be put around the allocator for basic_memory_buffer. |
include/fmt/core.h
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| #ifndef FMT_NO_UNIQUE_ADDRESS | ||
| # if FMT_HAS_CPP20_ATTRIBUTE(no_unique_address) | ||
| # define FMT_NO_UNIQUE_ADDRESS [[no_unique_address]] | ||
| # elif FMT_MSC_VERSION >= 1929 && FMT_CPLUSPLUS >= 202002L // VS2019 v16.10 and later | ||
| # define FMT_NO_UNIQUE_ADDRESS [[msvc::no_unique_address]] | ||
| # else | ||
| # define FMT_NO_UNIQUE_ADDRESS | ||
| # endif | ||
| #endif | ||
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Please move to format.h where it is used.
include/fmt/core.h
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| #define FMT_HAS_CPP20_ATTRIBUTE(attribute) \ | ||
| (FMT_CPLUSPLUS >= 202002L && FMT_HAS_CPP_ATTRIBUTE(attribute)) |
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I don't think we need this for a single check esp. since MSVC requires special handling. Let's just inline in the call site.
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Would it not be better to create this feature now, in the event that the other C++20 attributes (likely, unlikely) are desired in the future?
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There is little value in these variations of FMT_HAS_CPP_ATTRIBUTE so let's just inline.
This allows stateless allocators to take up no space while still avoiding the empty base class optimization.
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This allows stateless allocators to take up no space while still avoiding the empty base class optimization.