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template <class Rhs, class Ret=dont_care>
struct has_negate : public true_type-or-false_type {};

Inherits: If (i) rhs of type Rhs can be used in expression -rhs, and (ii) Ret=dont_care or the result of expression -rhs is convertible to Ret then inherits from true_type, otherwise inherits from false_type.

The default behaviour (Ret=dont_care) is to not check for the return value of prefix operator-. If Ret is different from the default dont_care type, the return value is checked to be convertible to Ret. Convertible to Ret means that the return value of the operator can be used as argument to a function expecting Ret:

void f(Ret);
Rhs rhs;
f(-rhs); // is valid if has_negate<Rhs, Ret>::value==true

If Ret=void, the return type is checked to be exactly void.

Header: #include <boost/type_traits/has_negate.hpp> or #include <boost/type_traits/has_operator.hpp> or #include <boost/type_traits.hpp>

Compiler Compatibility: Requires working SFINAE (i.e. BOOST_NO_SFINAE is not set). Only a minority of rather old compilers do not support this.


has_negate<Rhs, Ret>::value_type is the type bool.

has_negate<Rhs, Ret>::value is a bool integral constant expression.

has_negate<int>::value is a bool integral constant expression that evaluates to true.

has_negate<long> inherits from true_type.

has_negate<int, int> inherits from true_type.

has_negate<int, long> inherits from true_type.

has_negate<double, double> inherits from true_type.

has_negate<double, int> inherits from true_type.

has_negate<const int> inherits from true_type.

has_negate<int, std::string> inherits from false_type.

See also: Operator Type Traits

Known issues: