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

Subject: Re: [boost] [variant] Opinion on boost::safe_get<> and default boost::get<> behavior
From: Peter Dimov (lists_at_[hidden])
Date: 2014-12-09 14:44:32

Gottlob Frege wrote:
> My gut feeling is that "does this variant<X, Y> contain a Z" should be a 
> compile time error, because it obviously doesn't contain a Z.  (Of course 
> less obvious when variant<X,Y> is spelled 'T'.)

Or when it's spelled variant<T...>.

> And because it *can* be a compile time error.

Well yes, that is why we are having this discussion.

> In most C++ code, you need to go out of your way (eg dynamic_cast) to do 
> type-stuff at runtime.

get<> ALWAYS does type-stuff at runtime. It's not going to get any less 
runtimey. It's just going to catch a few (not very common) errors. It's 
still a dynamic_cast; the equivalent of the strict get<> would be a 
dynamic_cast that tells you, at compile time, "this cast will always fail, 
don't do it." Which, in dynamic_cast's case, is - I suspect - going to be a 
mixed blessing unless it's a warning, not an error.

That said, my recommendation still stands. Make get<> strict, see what 
happens.