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[SVN r1503]
This commit is contained in:
Jaakko Järvi
2003-09-05 18:22:13 +00:00
parent ef515c76c9
commit b007400de4
9 changed files with 150 additions and 22 deletions
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15
test/enable_if_lazy.cpp
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@@ -14,8 +14,8 @@
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_arithmetic.hpp>
using boost::enable_if;
using boost::enable_if_lazy;
using boost::enable_if_c;
using boost::lazy_enable_if_c;
using boost::is_arithmetic;
// This class provides a reduced example of a traits class for computing
@@ -43,26 +43,27 @@ struct mult_traits<double, double> {
// Next, a forwarding function mult() is defined. It is enabled only when
// mult_traits<T, U>::exists is true. The first version, using normal
// enable_if, works with only some compilers (it does not work in g++):
// enable_if_c, works with only some compilers (it does not work in g++):
#if 0
template <class T, class U>
typename enable_if<
typename enable_if_c<
mult_traits<T, U>::exists,
typename mult_traits<T, U>::type>::type
mult(const T& x, const U& y) {return x * y;}
#endif
// An improved version that works with more compilers uses enable_if_lazy.
// An improved version that works with more compilers uses lazy_enable_if_c.
// This template removes compiler errors from invalid code used as an
// argument to enable_if.
// argument to enable_if_c.
template <class T, class U>
typename enable_if_lazy<
typename lazy_enable_if_c<
mult_traits<T, U>::exists,
mult_traits<T, U> >::type
mult(const T& x, const U& y) {return x * y;}
int test_main(int, char*[])
{