EdenFS C++ Coding Conventions

Unless otherwise specified, defer to Meta C++ Coding Conventions and Meta C++ Style Guidelines.

Passing Parameters

Light Value Parameters

Lightweight value parameters are passed by value. These types fit in registers.

cpp

void take(int i, float f, char* p, std::string_view sv);

Light Owning Parameters

Lightweight owning types (e.g. std::string, std::vector, std::shared_ptr, folly::File, folly::Future) also fit in registers, but cannot be cheaply copied.

Unconditional ownership transfer to callee: by value

cpp

void take_ownership(folly::File f);

Temporary borrow: by const reference

cpp

void borrow(const folly::File& f);

Conditional ownership transfer: by rvalue reference

cpp

void maybe_take_ownership(folly::File&& f);

Why? Because passing ownership by value is more general and the temporary can be constructed directly on the stack: https://xania.org/202101/cpp-by-value-args.

Heavy Structs and Classes

For large structs and classes, owning or not, pass by const reference or rvalue reference. The cost of memcpy'ing the value on the stack can be nontrivial.

Type Parameters

Templates allow you to use perfect forwarding. Always write T&& and std::forward<T>.

template <typename... T>
void forwarding_call(T&&... args) {
    next_call(std::forward<T>(args)...);
}

Build Times

Forward-declare types when possible. Reducing the header include graph has a material effect on build times, especially when expensive headers such as windows.h can be avoided.

When possible, define any nontrivial function (or even members, with pImpl) in the .cpp file instead of the header. Remember that anything in a header is compiled N times, once for each including source.