Comment by rosshemsley | Hacker News Reader

Comment by rosshemsley | Hacker News Reader

Parent Full thread

One useful rule of thumb that works 99% of the time in C++11 is:

Never use "std::move"

It's really just there to allow fancy optimisations and you don't need it in most cases. You should rely on the sane defaults instead:

- Putting variables on the stack to manage object ownership/lifetime is a good default.

- Use std::unique_ptr or std::shared_ptr() for heap ownership (single ownership vs. shared)

- For a non-owning (mutable) reference, use const & (&) or const * (*) when the value may not exist.

- Always prefer passing by value (return types and parameters)

- If a parameter type is heavy, take a (const) reference.

- If the return type is heavy, the compiler's RVO will do its job.

No need to be more fancy than this

I disagree with you opinion on that. If you don't understand something doesn't mean that this is just for fancy optimizations.

Essentially you use std::move when you want to have pointer semantics without using a pointer. You don't want to use a pointers sometimes to keep objects on stack and use it to track ownership.

So instead of doing C* c1 = new C; C* c2 = c1; You have C c1; C c2 = c1; // here I have a move constructor which moves c1 to c2, c2 is now a null object.

This is what rust is able to do and you don't need expensive atomics (shared_ptr), ugly template syntax (unique_ptr), can keep everything on the stack and (!) have the objects be automatically cleaned up correctly.

> If you don't understand something doesn't mean that this is just for fancy optimizations.

You should definitely understand it, but if you find yourself wanting to use it, you should start by considering alternatives first. It's a sharp (and often unsafe) tool that should be avoided in most cases.

For your example, unique_ptr is the correct (and safe) solution and will do the same thing.

> you don't need expensive atomics (shared_ptr)

Note that shared_ptr provides no "atomicity". It is in reality exceptionally cheap.

Reply on news.ycombinator.com