82 lines
2.1 KiB
C++
82 lines
2.1 KiB
C++
#pragma once
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#include "utils/iterator/composable.hpp"
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#include "utils/iterator/iterator_base.hpp"
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namespace iter
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{
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// Class which maps values returned by I iterator into iterators of type J
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// ,which
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// return value of type T, with function OP.
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// function.
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// T - type of return value
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// I - iterator type
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// J - iterator type returned from OP
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// OP - type of mapper function
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template <class T, class I, class J, class OP>
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class FlatMap : public IteratorBase<T>,
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public Composable<T, FlatMap<T, I, J, OP>>
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{
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public:
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FlatMap() = delete;
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// FlatMap operation is designed to be used in chained calls which operate
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// on a
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// iterator. FlatMap will in that usecase receive other iterator by value
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// and
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// std::move is a optimization for it.
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FlatMap(I &&iter, OP &&op) : iter(std::move(iter)), op(std::move(op)) {}
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FlatMap(FlatMap &&m)
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: iter(std::move(m.iter)), op(std::move(m.op)),
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sub_iter(std::move(m.sub_iter))
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{
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}
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~FlatMap() final {}
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Option<T> next() final
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{
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do {
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if (!sub_iter.is_present()) {
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auto item = iter.next();
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if (item.is_present()) {
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sub_iter = Option<J>(op(item.take()));
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} else {
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return Option<T>();
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}
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}
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auto item = sub_iter.get().next();
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if (item.is_present()) {
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return std::move(item);
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} else {
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sub_iter.take();
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}
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} while (true);
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}
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Count count() final
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{
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// TODO: Correct count, are at least correcter
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return iter.count();
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}
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private:
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I iter;
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Option<J> sub_iter;
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OP op;
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};
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template <class I, class OP>
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auto make_flat_map(I &&iter, OP &&op)
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{
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// Compiler cant deduce type T and J. decltype is here to help with it.
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return FlatMap<decltype(op(iter.next().take()).next().take()), I,
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decltype(op(iter.next().take())), OP>(std::move(iter),
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std::move(op));
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}
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}
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