doc: Fix wrong code in WITH_LOCK doxygen comment #34355

what's the purpose of (j)?

It is used to explain &int, which is different than the int above.

Do you mean that

//!   WITH_LOCK(cs, int j = 1; return j);

wouldn't work, only

//!   WITH_LOCK(cs, int j = 1; return (j));

? Why do we need to group it, not sure I understand?

j is different than (j). One is int, the other is &int after decltype(auto) return type deduction

#include <type_traits>

#define WITH_CODE(code) [&]() -> decltype(auto) { code; }()

int main() {
    // Case 1: returns int (by value)
    static_assert(
        std::is_same_v<decltype(WITH_CODE(int i = 1; return i;)), int>);

    // Case 2: returns int& (reference to local variable)
    static_assert(
        std::is_same_v<decltype(WITH_CODE(int j = 1; return (j);)), int&>);

    // Compile-time check for reference-to-local
    static_assert(std::is_lvalue_reference_v<decltype(WITH_CODE(int k = 1;
                                                                return (k);))>);
}

https://godbolt.org/z/ez6d7dz3T

Also, with C++23, it will be int&&: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2266r3.html#decltype-auto

We usually don't have a ; inside, e.g.: https://github.com/bitcoin/bitcoin/blob/7f5ebef56a0f2bad7df30252b11da3e33cb3c144/src/net.h#L429

Correct. However, the docs here exist to explain decltype(auto).

i guess i didn't understand the comment here. the first semicolon is required, but the second can be removed, so i did that