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[section:function_output Function Output Iterator]
The function output iterator adaptor makes it easier to create custom
output iterators. The adaptor takes a unary function and creates a
model of Output Iterator. Each item assigned to the output iterator is
passed as an argument to the unary function. The motivation for this
iterator is that creating a conforming output iterator is non-trivial,
particularly because the proper implementation usually requires a
proxy object.
[h2 Example]
struct string_appender
{
string_appender(std::string& s)
: m_str(&s)
{}
void operator()(const std::string& x) const
{
*m_str += x;
}
std::string* m_str;
};
int main(int, char*[])
{
std::vector<std::string> x;
x.push_back("hello");
x.push_back(" ");
x.push_back("world");
x.push_back("!");
std::string s = "";
std::copy(x.begin(), x.end(),
boost::make_function_output_iterator(string_appender(s)));
std::cout << s << std::endl;
return 0;
}
[h2 Reference]
[h3 Synopsis]
template <class UnaryFunction>
class function_output_iterator {
public:
typedef std::output_iterator_tag iterator_category;
typedef void value_type;
typedef void difference_type;
typedef void pointer;
typedef void reference;
explicit function_output_iterator();
explicit function_output_iterator(const UnaryFunction& f);
/* see below */ operator*();
function_output_iterator& operator++();
function_output_iterator& operator++(int);
private:
UnaryFunction m_f; // exposition only
};
[h3 Requirements]
`UnaryFunction` must be Assignable and Copy Constructible.
[h3 Concepts]
`function_output_iterator` is a model of the Writable and
Incrementable Iterator concepts.
[h3 Operations]
explicit function_output_iterator(const UnaryFunction& f = UnaryFunction());
[*Effects: ] Constructs an instance of `function_output_iterator`
with `m_f` constructed from `f`.
unspecified_type operator*();
[*Returns: ] An object `r` of unspecified type such that `r = t`
is equivalent to `m_f(t)` for all `t`.
function_output_iterator& operator++();
[*Returns: ] `*this`.
function_output_iterator& operator++(int);
[*Returns: ] `*this`.
[endsect]
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