Rene Rivera <grafik.list@redshift-software.com> writes:
Daniel Wallin wrote:
I don't think the rationale for this is completely expressed in the docs. The reason binding<> works like this is because of dangling references to defaults. Consider from your example above:
something_t const & q = args[something | 0];
When binding<> returns the default type here you will get a dangling reference here:
int const& = args[something | 0]
Our design handles this by letting binding<> return a reference type when an argument is bound to the keyword, and otherwise return the default type unchanged.
OK I understand what you are saying, but I don't see it :-) As far as I understand from the docs the binding<>::type has nothing to do with the default value as above as it happens before one gets to extracting the value. I wasn't talking about changing the types that the operator[] return.
Consider the usage you're proposing when you /do/ want a reference to bind to the actual argument: typename binding<Args,tag::k,int>::type const& x = args[k | 0] If the "k" argument wasn't supplied, your int const& will be a dangling reference. -- Dave Abrahams Boost Consulting www.boost-consulting.com