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- [/
- (C) Copyright 2009-2011 Frederic Bron.
- Distributed under the Boost Software License, Version 1.0.
- (See accompanying file LICENSE_1_0.txt or copy at
- http://www.boost.org/LICENSE_1_0.txt).
- ]
- [section:has_less has_less]
- template <class Lhs, class Rhs=Lhs, class Ret=dont_care>
- struct has_less : public __tof {};
- __inherit
- If (i) `lhs` of type `Lhs` and `rhs` of type `Rhs` can be used in expression `lhs<rhs`,
- and (ii) `Ret=dont_care` or the result of expression `lhs<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 binary `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);
- Lhs lhs;
- Rhs rhs;
- f(lhs<rhs); // is valid if has_less<Lhs, Rhs, Ret>::value==true
- ``
- If `Ret=void`, the return type is checked to be exactly `void`.
- __header `#include <boost/type_traits/has_less.hpp>` or `#include <boost/type_traits/has_operator.hpp>` or `#include <boost/type_traits.hpp>`
- [has_binary_operator_compat]
- __examples
- [:`has_less<Lhs, Rhs, Ret>::value_type` is the type `bool`.]
- [:`has_less<Lhs, Rhs, Ret>::value` is a `bool` integral constant expression.]
- [:`has_less<int>::value` is a `bool` integral constant expression that evaluates to `true`.]
- [:`has_less<long>` inherits from `__true_type`.]
- [:`has_less<int, int, bool>` inherits from `__true_type`.]
- [:`has_less<int, double, bool>` inherits from `__true_type`.]
- [:`has_less<const int>` inherits from `__true_type`.]
- [:`has_less<int*, int>` inherits from `__false_type`.]
- [:`has_less<int*, double*>` inherits from `__false_type`.]
- [:`has_less<int, int, std::string>` inherits from `__false_type`.]
- [*See also:] [link boost_typetraits.category.value_traits.operators Operator Type Traits]
- [binary_operator_known_issues has_less..<..bool..bool..const ]
- [endsect]
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