Re: [Boost-users] shared_ptr as reference argument

Emil, I know that the second snippet is illegal in C++, but your statement was that const is only a part of type system and has no impact on optimization, I just answered you with my doubts, and made a first obvious example with NRVO, which highly depends on const. const might also involve some optimizations, e.g. in multi-threaded context. Let's imagine a value being passed to a function by const reference. This function starts 2 or more threads and passes the value to them as reference to a const object as well. What happens in this context? As long it is not volatile it might be cached in a register, but I think that if the value is const, compiler has stronger assumption, that this value is good enough to be cached for all threads... On Fri, Mar 20, 2009 at 1:56 AM, Emil Dotchevski wrote:

On Thu, Mar 19, 2009 at 4:29 PM, Ovanes Markarian wrote:

...

What about RVO and NRVO?

You still can bind a temporary to a const reference. This is a simple example on how it is possible to do optimizations. Or am I mistaken?

Example:

std::string foo();

void bar() { std::string const& bound_temporary = foo();

std::cout << bound_temporary; }

whereas this is invalid:

void invalid_bar() { std::string& bound_temporary = foo(); //will not work, but AFAIK some compilers support it }

Right, your first snippet is valid and the second is ill-formed.

...

So compilers can do optimizations based on constness.

What optimizations do you have in mind? The second snippet is simply illegal C++ (should not compile.)

Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users