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70d1adfe4b
* save format string for NetException * format exceptions * format exceptions 2 * format exceptions 3 * format exceptions 4 * format exceptions 5 * format exceptions 6 * fix * format exceptions 7 * format exceptions 8 * Update MergeTreeIndexGin.cpp * Update AggregateFunctionMap.cpp * Update AggregateFunctionMap.cpp * fix
169 lines
4.5 KiB
C++
169 lines
4.5 KiB
C++
#pragma once
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#include <base/demangle.h>
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#include <base/TypeList.h>
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#include <Common/Exception.h>
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#include <typeinfo>
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/* Generic utils which are intended for visitor pattern implementation.
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* The original purpose is to provide possibility to get concrete template specialisation for type in list.
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*
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* Usage:
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* 1. Declare visitor interface base class for types T_1, ..., T_N:
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* class MyVisitor : public Visitor<T_1, ..., T_N> {};
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* 2. Declare visitor implementation base class using VisitorImpl:
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* template <typename Derived>
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* class MyVisitorImpl : public VisitorImpl<Derived, MyVisitor> {};
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* 3. Add virtual function 'accept' to common base of T_1, ..., T_N:
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* class T_Base
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* {
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* ...
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* public:
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* virtual void accept(MyVisitor &) { throw Exception("Accept not implemented"); }
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* };
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* 4. Declare base class for T_1, ..., T_N implementation:
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* template <typename Derived>
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* class T_Impl : public Visitable<Derived, T_Base, MyVisitor> {};
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* 5. Implement 'accept' for each T_i:
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* a) inherit from T_Impl:
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* class T_i : public T_Impl<T_i> { ... };
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* b) or in order to avoid ambiguity:
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* class T_i
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* {
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* ...
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* public:
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* void accept(MyVisitor & visitor) override { visitor.visit(*this); }
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* };
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* 6. Implement concrete visitor with visitImpl template function:
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* class MyConcreteVisitor : public MyVisitorImpl<MyConcreteVisitor>
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* {
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* ...
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* public:
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* template <typename T>
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* void visitImpl(T & t) { ... }
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* };
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* 7. Now you can call concrete implementation for MyConcreteVisitor:
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* MyConcreteVisitor visitor;
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* T_Base * base;
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* base->accept(visitor); /// call MyConcreteVisitor::visitImpl(T & t)
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*
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* TODO: Add ConstVisitor with 'visit(const Type &)' function in order to implement 'accept(...) const'.
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*/
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namespace DB
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{
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namespace ErrorCodes
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{
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extern const int LOGICAL_ERROR;
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}
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template <typename ... Types>
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class Visitor;
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template <>
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class Visitor<>
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{
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public:
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using List = TypeList<>;
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protected:
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~Visitor() = default;
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};
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template <typename Type>
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class Visitor<Type> : public Visitor<>
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{
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public:
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using List = TypeList<Type>;
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virtual void visit(Type &) = 0;
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protected:
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~Visitor() = default;
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};
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template <typename Type, typename ... Types>
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class Visitor<Type, Types ...> : public Visitor<Types ...>
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{
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public:
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using List = TypeList<Type, Types ...>;
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using Visitor<Types ...>::visit;
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virtual void visit(Type &) = 0;
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protected:
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~Visitor() = default;
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};
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template <typename Derived, typename VisitorBase, typename ... Types>
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class VisitorImplHelper;
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template <typename Derived, typename VisitorBase>
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class VisitorImplHelper<Derived, VisitorBase> : public VisitorBase
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{
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protected:
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~VisitorImplHelper() = default;
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};
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template <typename Derived, typename VisitorBase, typename Type>
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class VisitorImplHelper<Derived, VisitorBase, Type> : public VisitorBase
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{
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public:
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using VisitorBase::visit;
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void visit(Type & value) override { static_cast<Derived *>(this)->visitImpl(value); }
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protected:
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template <typename T>
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void visitImpl(Type &)
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{
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throw Exception(ErrorCodes::LOGICAL_ERROR, "visitImpl({} &) is not implemented for class{}",
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demangle(typeid(T).name()), demangle(typeid(Derived).name()));
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}
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~VisitorImplHelper() = default;
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};
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template <typename Derived, typename VisitorBase, typename Type, typename ... Types>
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class VisitorImplHelper<Derived, VisitorBase, Type, Types ...>
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: public VisitorImplHelper<Derived, VisitorBase, Types ...>
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{
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public:
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using VisitorImplHelper<Derived, VisitorBase, Types ...>::visit;
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void visit(Type & value) override { static_cast<Derived *>(this)->visitImpl(value); }
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protected:
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template <typename T>
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void visitImpl(Type &)
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{
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throw Exception(ErrorCodes::LOGICAL_ERROR, "visitImpl({} &) is not implemented for class{}",
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demangle(typeid(T).name()), demangle(typeid(Derived).name()));
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}
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~VisitorImplHelper() = default;
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};
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template <typename Derived, typename VisitorBase>
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class VisitorImpl : public
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TypeListChangeRoot<
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VisitorImplHelper,
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TypeListConcat<
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TypeList<Derived, VisitorBase>,
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typename VisitorBase::List
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>
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>
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{
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protected:
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~VisitorImpl() = default;
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};
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template <typename Derived, typename Base, typename Visitor>
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class Visitable : public Base
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{
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public:
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void accept(Visitor & visitor) override { visitor.visit(*static_cast<Derived *>(this)); }
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};
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}
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