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chriskohlhoff / asio

Asio C++ Library
http://think-async.com/Asio
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Add constexpr support to ip::address* and ip::network* classes #1276

Open rcombs opened 1 year ago

rcombs commented 1 year ago

This is split into 2 segments: implementation changes that make the code more constexpr-compatible, and changes that actually add constexpr tags. The new functionality is unit-tested extensively. Most functions are only made constexpr when building header-only, since they're either defined in .ipp files or depend on functions that are.

rcombs commented 1 year ago

The initial version of this PR ran into some issues on the CI due to Windows using a union type for in_addr, where the 32-bit int member doesn't come first. This seems to make it impossible to initialize and assign to in constexpr code pre-C++20. The current version addresses this largely by requiring C++20 for constexpr on address_v4.

This could alternately be addressed by using bytes_type as the internal storage format for address_v4, and bit-casting/memcpying to/from in_addr when calling inet_pton and inet_ntop. This could also be applied to IPv6; in both cases, it'd allow us to support constexpr on older C++ versions; it should be ABI-compatible with the existing code, though it's possible that some cursed platform out there has auxiliary padding or some other nonsense in the in[6]_addr structs.