or_

Synopsis

template< 
      typename F1
    , typename F2
    ...
    , typename Fn = unspecified
    >
struct or_
{
    typedef unspecified type;
};

Description

Returns the result of short-circuit logical or (||) operation on its arguments.

Header

#include <boost/mpl/or.hpp>
#include <boost/mpl/logical.hpp>

Parameters

Parameter	Requirement	Description
`F1`, `F2`,... `Fn`	Nullary Metafunction	Operation's arguments.

Expression semantics

For arbitrary nullary Metafunctions f1, f2,... fn:

typedef or_<f1,f2,...,fn>::type r;

Return type:	Integral Constant.
Semantics:	`r` is `true_` if either of `f1::type::value`, `f2::type::value`,... `fn::type::value` expressions evaluates to `true`, and `false_` otherwise; guarantees left-to-right evaluation; the operands subsequent to the first `f`i metafunction that evaluates to `true` are not evaluated.

typedef or_<f1,f2,...,fn> r;

Return type: Integral Constant.

Semantics:

Equivalent to

struct r : or_<f1,f2,...,fn>::type {};

Example

struct unknown;

BOOST_MPL_ASSERT(( or_< true_,true_ > ));
BOOST_MPL_ASSERT(( or_< false_,true_ > ));
BOOST_MPL_ASSERT(( or_< true_,false_ > ));
BOOST_MPL_ASSERT_NOT(( or_< false_,false_ > ));
BOOST_MPL_ASSERT(( or_< true_,unknown > )); // OK
BOOST_MPL_ASSERT(( or_< true_,unknown,unknown > )); // OK too