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What are the rules/limitations of constexpr functions? What is consteval (C++20)? What is constinit (C++20)? How does constexpr improve performance? Can constexpr be used with classes and containers? What is 'if constexpr' and why is it useful? What is template metaprogramming versus constexpr for compile-time work?
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What is compile-time computation good for, and what are its trade-offs?

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Moving work to compile time (via constexpr/consteval, templates) removes runtime cost, enables constants for array sizes and template arguments, and can catch errors earlier. Trade-offs include longer compile times, increased code/complexity, and debugging difficulty of compile-time logic. It's most valuable for hot constants, lookup tables, and configuration known at build time.
constexpr auto table = makeSineTable();  // built at compile time
Real-world example Precomputing a CRC or sine table at compile time eliminates its runtime initialization cost.

Common follow-ups: What are the costs of heavy compile-time computation? | When is it worthwhile?

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All 11 Constexpr & Compile-Time questions