What's the best practice for creating instances of a struct?

Question

I'm trying to understand what's the best practice for creating instances of a struct. In C++ I'd pass everything I need to the constructor and throw an exception if the struct could not be created. In rust I've been told to create a method that returns a Result. But isn't this too much work? Why not just fail!()?

Also, if returning Result is the way to go, does this mean that all structs will need a factory?

Answer 1

A basic constructor for YourStruct should be a static method called YourStruct::new() (see the Rust style guidelines for more info).

For the return type, use YourStruct if nothing can go wrong or if you use fail!(). Use Option<YourStruct> if there's only one obvious reason for the constructor failing. Use Result<YourStruct, YourStructErr> if it would be helpful to the caller to know why it failed. The problem with fail!() is it doesn't give the caller a chance to try again, or pass a nice error message back to the user, or whatever else the caller might want to do. In certain situations, fail!() might be okay.