TakeWhile.h

#pragma once
 
#include <utility>
#include <optional>
#include <algorithm>
 
#include "../Common.h"
#include "../util/TraitImpl.h"
 
namespace CXXIter {
 
    // ################################################################################################
    // TAKE WHILE
    // ################################################################################################
    namespace op {
        template<typename TChainInput, typename TTakePredicate>
        class [[nodiscard(CXXITER_CHAINER_NODISCARD_WARNING)]] TakeWhile : public IterApi<TakeWhile<TChainInput, TTakePredicate>> {
            friend struct trait::Iterator<TakeWhile<TChainInput, TTakePredicate>>;
        private:
            TChainInput input;
            TTakePredicate takePredicate;
        public:
            constexpr TakeWhile(TChainInput&& input, TTakePredicate takePredicate) : input(std::move(input)), takePredicate(takePredicate) {}
        };
    }
    // ------------------------------------------------------------------------------------------------
    template<typename TChainInput, typename TTakePredicate>
    struct trait::Iterator<op::TakeWhile<TChainInput, TTakePredicate>> {
        using ChainInputIterator = trait::Iterator<TChainInput>;
        using InputItem = typename TChainInput::Item;
        // CXXIter Interface
        using Self = op::TakeWhile<TChainInput, TTakePredicate>;
        using Item = InputItem;
 
        static constexpr inline IterValue<Item> next(Self& self) {
            auto item = ChainInputIterator::next(self.input);
            if(!item.has_value()) [[unlikely]] { return {}; }
            // end iterator directly after takePredicate returned false the first time
            if(self.takePredicate(item.value()) == false) { return {}; }
            return item;
        }
        static constexpr inline SizeHint sizeHint(const Self& self) {
            SizeHint input = ChainInputIterator::sizeHint(self.input);
            return SizeHint(0, input.upperBound);
        }
        static constexpr inline size_t advanceBy(Self& self, size_t n) { return util::advanceByPull(self, n); }
    };
 
}