C++ Compile-Time Programming | `constexpr`, `consteval`, and TMP

constexpr basics

constexpr int square(int x) {
    return x * x;
}

int main() {
    constexpr int result = square(5);
    int arr[result];
    
    int x = 10;
    int result2 = square(x);  // may run at runtime
}

constexpr variables & classes

Illustrative Point with constexpr constructor and methods—same as original.

if constexpr (C++17)

See dedicated article: if constexpr.

consteval (C++20)

See consteval.

Examples

Compile-time string hashing, Fibonacci arrays, type checks, sorting constexpr arrays—code mirrors the Korean post.

Template metaprogramming

Factorial struct recursion and simple type lists demonstrate classic TMP; prefer constexpr algorithms when possible for readability.

Performance comparison

Illustrates runtime vs compile-time Fibonacci to motivate where work happens—not a substitute for Big-O analysis of algorithms.

Pitfalls

constexpr restrictions (e.g. no static locals in older rules—check your standard version), runtime inputs, and exponential compile-time recursion.

constexpr vs consteval vs const

const is not necessarily compile-time; constexpr/consteval express stronger guarantees.

FAQ

Topics: when to use constexpr, relation to inline, compile-time cost, C++20 improvements, TMP vs constexpr readability.

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Related posts

• constexpr functions
• if constexpr
• Constexpr basics series

Keywords

C++, constexpr, compile-time, TMP, metaprogramming.

See also

• Compile-time optimization series