75 lines
1.3 KiB
C++
75 lines
1.3 KiB
C++
#ifndef SELECT_H_
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#define SELECT_H_
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#include <boost/utility/result_of.hpp>
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template<typename Source, typename Fn>
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class Select
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{
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public:
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typedef typename boost::result_of<Fn(typename Source::ElementType&)>::type ElementType;
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typedef typename Source::MarkerType MarkerType;
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public:
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Select(Source source, Fn fn)
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: source(source), fn(fn)
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{
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}
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bool step()
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{
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if(!this->source.step() )
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return false;
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this->current = this->fn(*this->source.get() );
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return true;
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}
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ElementType* get()
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{
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return ¤t;
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}
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MarkerType mark() const
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{
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return this->source.mark();
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}
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void restore(MarkerType mark)
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{
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this->source.restore(mark);
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this->current = this->fn(*this->source.get() );
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}
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private:
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Source source;
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Fn fn;
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ElementType current;
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};
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namespace db {
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template<typename Pred>
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struct SelectOp
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{
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Pred pred;
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template<typename Source>
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friend Select<Source, Pred> operator|(Source source, const SelectOp& op)
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{
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return Select<Source, Pred>(source, op.pred);
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}
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};
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template<typename Pred>
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inline SelectOp<Pred> select(Pred pred)
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{
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SelectOp<Pred> result = {pred};
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return result;
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}
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}
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#endif
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