Re: [boost] [optional] Safe optional

On Sun, 16 Nov 2014 23:04:43 -0800, Andrzej Krzemienski wrote:

Hi Everyone, I would like to run an idea through everyone in this list. There is a recurring complaint about Boost.Optional that it allows you to do "unsafe" things: 1. Inadvertent mixed comparisons between T and optional<T> 2. Unintended conversion from T to optional<T>

The problem with optional is that it tries to be a drop-in replacement proxy for its underlying type, and, unfortunately, it can't fully do that. So it ends up with an identity crisis. IMO, optional should be treated as a first class object, not a thin wrapper around T, that means no implicit conversions to/from T, no implicit comparisons with T, etc... Last time I looked at this, that will solve the reference rebinding gotcha. That is, you'll have one behavior for optional<T> and optional. It will also solve the following gotcha too: optional<bool> b(false); if(b == true) { // Does not get executed. std::cout << "???\n"; } if(b) { // Gets executed. std::cout << "!!!\n"; } which I believe to be an ever bigger problem. In short, and IMHO optional should be a true model of the pointer concept, like iterators and shared_ptr.