Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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has_pre_increment

template <class Rhs, class Ret=dont_care>
struct has_pre_increment : 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_pre_increment<Rhs, Ret>::value==true

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

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

Examples:

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

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

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

has_pre_increment<long> inherits from true_type.

has_pre_increment<int, int> inherits from true_type.

has_pre_increment<int, long> inherits from true_type.

has_pre_increment<double, double> inherits from true_type.

has_pre_increment<double, int> inherits from true_type.

has_pre_increment<bool> inherits from true_type.

has_pre_increment<const int> inherits from false_type.

has_pre_increment<void*> inherits from false_type.

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

See also: Operator Type Traits

Limitation:

Known issues:


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