move-copy-semantics

Move & Copy Semantics

std::move(x) is only a cast to T&&. When x is const& (or const), it yields a const T&& that binds to the copy constructor, not the move constructor — so it compiles, looks like a move, and silently deep-copies. This is the bug that made Request/RequestState construction copy their whole payload.

• Never std::move a const& / const value. The two ingredients of the bug are always "a const source + std::move". Don't combine them.
• Sink parameters go by value + std::move. If a function/ctor retains its argument, take it by value and std::move it into the member. Use const& only for parameters you read but do not retain.
• Make callers move. Pass std::move(local) when you hand an owned local to a sink parameter and don't use it afterwards; an lvalue silently copies.
• Consider making heavy, rarely-copied domain types move-only (= delete copy) with an explicit clone(), so an accidental copy is a compile error.

// Bad – const& + std::move => copies
Request(const RequestState& state) : state_(std::move(state)) {}

// Good – sink by value; caller chooses copy (lvalue) vs move (std::move)
Request(RequestState state) : state_(std::move(state)) {}

clang-tidy's performance-move-const-arg (see repo .clang-tidy) flags this.