Re: [boost] [variant] Opinion on boost::safe_get<> and default boost::get<> behavior

Le 09/12/14 18:39, Peter Dimov a écrit :

Antony Polukhin wrote: ...

...

boost::variant v(100);

boost::safe_get<bool>(&v); // compile time error boost::safe_get<bool>(v); // compile time error boost::unsafe_get<bool>(&v); // returns NULL instead of compile time error boost::unsafe_get<bool>(v); // throws exception on runtime instead of compile time error

I'm in doubt, what the default behavior of boost::get must be: * safe_get behavior is much closer to Standard Library behavior (just like std::get for tuples) and allows to avoid errors in user code * unsafe_get behavior is same as behavior of old boost::get and won't break user's code if boost::get is used in some generic contexs

What's your opinion?

My opinion is that these functions are misnamed. unsafe_get is not unsafe. I'd say that they are strict and relaxed, respectively, not safe and unsafe.

Regarding the default, there's only one way to find out. Namely, you switch boost::get to be strict, then see if there are any complaints. (Having the default be relaxed doesn't seem to make much sense.)

There's nothing wrong (or unsafe) with the old behavior - it consistently answers the question "does v contain a T" - so the decision can't be made based on principles alone and must be informed by practice. That is, do the benefits of the strict get - which are pretty much only catching your typo when you say get<T>(v) instead of get<T>(w) - outweigh the loss of functionality.

I agree with peter strict/relaxed covers better the Even if changing the default behavior to strict_get could break some user code, this will result on a compile error, which wouldn't be a silent break. If you provide both strict/relaxed versions, the user could always change its defaulted get<bool>(v) to relaxed_get(bool)(v). Best, Vicente P.S. I don't think there will be too much uses of relaxed_get, but who know what C++ programmers use ;-)