Re: [Boost-users] boost variant compile time visitation: verification

Subject: Re: [Boost-users] boost variant compile time visitation: verification
From: Hicham Mouline (hicham_at_[hidden])
Date: 2009-04-21 11:04:08

This sentence from the doc

 

Notable features of
<http://www.boost.org/doc/libs/1_38_0/doc/html/boost/variant.html>
boost::variant include:

*	Full value semantics, including adherence to standard overload
resolution rules for conversion operations.
*	Compile-time type-safe value visitation via
<http://www.boost.org/doc/libs/1_38_0/doc/html/boost/apply_visitor.html>
boost::apply_visitor.

is confusing to me.

 

I was gonna ask if there was a purely compile-time visitor, but that doesn't
make sense,

as the instance of the variant can be assigned any of the bounded types at
runtime.

 

Regards,

 

 

 

 

From: boost-users-bounces_at_[hidden]
[mailto:boost-users-bounces_at_[hidden]] On Behalf Of Ovanes Markarian
Sent: 21 April 2009 15:25
To: boost-users_at_[hidden]
Subject: Re: [Boost-users] boost variant compile time visitation:
verification

 

Hicham,

visitation is not done at compile-time. Doc states as far as I remember that
the compiler might (with high probability) inline the calls, so that they
have similar performance as a switch statement. Switch usually equals to a
jump in assembler. But there must be runtime overhead, since you put at
runtime object instances into the variant.

Greetings,
Ovanes