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