2003-03-12 13:29:12 +00:00
<!doctype html public "-//ietf//dtd html//en">
< html >< head >< title > boost::mpl::or_</ title >
< link rel = "stylesheet" href = "../mpl_wiki.css" >
</ head >< body bgcolor = "white" >
< h1 >< a href = "../Table_of_Contents.html" >< img src = "../mpl_logo.jpg" alt = "[Home]" border = 0 align = "right" ></ a > or_</ h1 >< h3 > Synopsis</ h3 >
< p >
< pre >
template<
typename F1
, typename F2
, typename F3 = false_
...
, typename Fn = false_
>
struct or_
{
typedef < em > unspecified</ em > type;
};
</ pre >
< p >
< h3 > Description</ h3 >
< p >
Returns the result of short-circuit < em > logical or</ em > (< code > ||</ code > ) operation on its arguments.
< p >
< h3 > Definition</ h3 >
< p >
< pre >
#include "< a href = "../../../../../boost/mpl/or.hpp" > boost/mpl/or.hpp</ a > "
</ pre >
< p >
< h3 > Parameters</ h3 >
< table border = "1" >
< tr >< th > Parameter </ th >< th > Requirement </ th >< th > Description </ th ></ tr >
< tr >< td >< code > F1, F2, .., Fn</ code ></ td >< td > A model of nullary < a href = "../Metafunction.html" > Metafunction</ a ></ td >< td ></ td ></ tr >
</ table >
< p >
< h3 > Expression semantics</ h3 >
< p >
< table border = "1" >
< tr >< th > Expression </ th >< th > Expression type </ th >< th > Precondition </ th >< th > Semantics </ th >< th > Postcondition </ th ></ tr >
2003-11-12 07:55:12 +00:00
< tr >< td >< code > or_< f1,f2,..,fn> </ code ></ td >< td > A model of < code > bool</ code > < a href = "../Integral_Constant.html" > Integral Constant</ a ></ td >< td ></ td >< td >< code > true_</ code > if either of < code > f1::type::value, f2::type::value, .., fn::type::value</ code > expressions evaluates to true, and < code > false_</ code > otherwise; guarantees left-to-right evaluation; moreover, the operands subsequent to the first < code > fi</ code > metafunction that evaluates to true are not evaluated.</ td >< td ></ td ></ tr >
2003-03-12 13:29:12 +00:00
</ table >
< p >
< h3 > Example</ h3 >
< p >
< pre >
< span class = "cxx-comment" > // will generate compile-time error if invoked with T == any fundamental type</ span >
template< typename T > struct fail
{
typedef typename T::nonexistent type;
};
< p >
2003-11-12 07:55:12 +00:00
BOOST_STATIC_ASSERT((or_< false_,true_ > ::value == true));
BOOST_STATIC_ASSERT((or_< true_,fail< int> > ::value == true)); < span class = "cxx-comment" > // OK, fail< int> is never invoked</ span >
BOOST_STATIC_ASSERT((or_< false_,true_,fail< int> > ::value == true)); < span class = "cxx-comment" > // OK too</ span >
2003-03-12 13:29:12 +00:00
</ pre >
< p >
< h3 > See also</ h3 >
< p >
< a href = "../Metafunctions.html" > Metafunctions</ a > , < code >< a href = "../Reference/and.html" > and_</ a ></ code > , < code >< a href = "../Reference/not.html" > not_</ a ></ code >
< p >< hr >
2003-11-12 07:55:12 +00:00
< a href = "../Table_of_Contents.html" > Table of Contents</ a >< br > Last edited September 6, 2003 3:14 am</ body ></ html >
