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40 lines
1.0 KiB
C++
40 lines
1.0 KiB
C++
#pragma once
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#include <DB/Functions/IFunction.h>
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#include <common/singleton.h>
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namespace DB
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{
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class Context;
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/** Creates function by name.
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* Function could use for initialization (take ownership of shared_ptr, for example)
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* some dictionaries from Context.
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*/
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class FunctionFactory : public Singleton<FunctionFactory>
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{
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friend class StorageSystemFunctions;
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private:
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typedef FunctionPtr (*Creator)(const Context & context); /// Not std::function, for lower object size and less indirection.
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std::unordered_map<String, Creator> functions;
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public:
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FunctionFactory();
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FunctionPtr get(const String & name, const Context & context) const; /// Throws an exception if not found.
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FunctionPtr tryGet(const String & name, const Context & context) const; /// Returns nullptr if not found.
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/// No locking, you must register all functions before usage of get, tryGet.
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template <typename F> void registerFunction()
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{
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static_assert(std::is_same<decltype(&F::create), Creator>::value, "F::create has incorrect type");
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functions[F::name] = &F::create;
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}
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};
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}
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