On Thu, May 12, 2011 at 12:05 PM, lcaminiti <lorcaminiti@gmail.com> wrote:
Jeffrey Lee Hellrung, Jr.-2 wrote:
On Thu, May 12, 2011 at 11:16 AM, lcaminiti <lorcaminiti@gmail.com
>
wrote:
Jeffrey Lee Hellrung, Jr.-2 wrote:
[...]
I would infer from this and the documentation that
const bind(const int&) factor // outer const superfluous??? bind(const int&) factor const bind(const int)& factor // outer const superfluous??? bind(const int)& factor const bind(int)& factor bind(const int&) const factor // outer const superfluous??? bind(int) const & factor
are all equivalent, but I'm not sure. Can you please clarify in the documentation?
[...snip rest of example...]
Yes, the Tutorial section already mentions that: 1) const must always appear before bind when constant binding is used so bind ... const is not valid (this is just for simplicity, the macros could be programmed to accepts both const bind and bind const). 2) when const bind is used on a variable that is already const the bind's const has no effect.
So that addresses the placement of const; the '&' can also either be put inside or outside the bind(...), right?
No. References are bound be value when bind is used without the trailing &:
int y = 0; int& x = y BOOST_LOCAL_BLOCK(bind x) { // by val x = 0; // Has only local effect (outer x and y are not changed). } BOOST_LOCAL_BLOCK(bind& x) { // by ref x = 0; // Has effect on enclosing scope (outer x and y are changed). }
This is how Boost.ScopeExit bind semantic works and it made sense to me because it allows to bind references by both value and reference (and not just by reference). I can spell this out more clearly in the docs.
I meant to explicitly ask whether the following are equivalent: bind(T)& x bind(T&) x [...]
Also, what about commas from template instantiations? E.g., does
bind(tmpl<T1,T2>) x
work?
Yes but you have to use BOOST_IDENTITY_TYPE (its a macro of Boost.Local that I'd eventually propose to add to under boost/utility). It's explained in the Advanced Topics section:
http://svn.boost.org/svn/boost/sandbox/local/libs/local/doc/html/boost_local...
For example:
bind(BOOST_IDENTITY_TYPE((std::map<std::string, double>))) x
This works (on ISO C++, no variadics required). Note the extra set of parenthesis needed around the type-with-commas within the macro parenthesis BOOST_IDENTITY_TYPE((type_with_commas)) -- it expands to something like function_traits<void(type_with_commas)>::arg1_type.
Sounds good. - Jeff