57 lines
1.7 KiB
C++
57 lines
1.7 KiB
C++
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#pragma once
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#include <memory>
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#include <vector>
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#include "query/typed_value.hpp"
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#include "utils/memory.hpp"
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namespace query {
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/**
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* `AnyStream` can wrap *any* type implementing the `Stream` concept into a
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* single type.
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*
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* The type erasure technique is used. The original type which an `AnyStream`
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* was constructed from is "erased", as `AnyStream` is not a class template and
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* doesn't use the type in any way. Client code can then program just for
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* `AnyStream`, rather than using static polymorphism to handle any type
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* implementing the `Stream` concept.
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*/
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class AnyStream final {
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public:
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template <class TStream>
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AnyStream(TStream *stream, utils::MemoryResource *memory_resource)
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: content_{utils::Allocator<GenericWrapper<TStream>>{memory_resource}
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.template new_object<GenericWrapper<TStream>>(stream),
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[memory_resource](Wrapper *ptr) {
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utils::Allocator<GenericWrapper<TStream>>{memory_resource}
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.template delete_object<GenericWrapper<TStream>>(
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static_cast<GenericWrapper<TStream> *>(ptr));
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}} {}
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void Result(const std::vector<TypedValue> &values) {
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content_->Result(values);
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}
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private:
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struct Wrapper {
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virtual void Result(const std::vector<TypedValue> &values) = 0;
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};
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template <class TStream>
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struct GenericWrapper final : public Wrapper {
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explicit GenericWrapper(TStream *stream) : stream_{stream} {}
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void Result(const std::vector<TypedValue> &values) override {
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stream_->Result(values);
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}
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TStream *stream_;
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};
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std::unique_ptr<Wrapper, std::function<void(Wrapper *)>> content_;
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};
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} // namespace query
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