On Sunday 24 November 2024 05:18:33 Pacific Standard Time Volker Hilsheimer via Interest wrote: > Also, some things that are constexpr in a test might not be constexpr in a > real program. E.g. std::string can only be constexpr as long as the string > fits into whatever size the library uses for its small-string optimization. > As soon as that space is not sufficient, std::string has to allocate using > operator new, and your code will no longer build.
C++20 does support dynamic memory allocation at constexpr time https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0784r7.html It must be freed before the evaluation terminates, though. We can detect std::is_constant_evaluated() and use calls to new instead of QArrayData::allocate, but every use of std::is_constant_evaluated() implies that the code that was checked at constexpr time is not the code that is run at runtime. -- Thiago Macieira - thiago.macieira (AT) intel.com Principal Engineer - Intel DCAI Platform & System Engineering
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