ClickHouse/dbms/src/Functions/FunctionFactory.h

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#pragma once
#include <Functions/IFunction.h>
#include <Common/IFactoryWithAliases.h>
#include <ext/singleton.h>
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#include <functional>
#include <memory>
#include <string>
#include <unordered_map>
namespace DB
{
class Context;
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/** Creates function by name.
* Function could use for initialization (take ownership of shared_ptr, for example)
* some dictionaries from Context.
*/
class FunctionFactory : public ext::singleton<FunctionFactory>, public IFactoryWithAliases<std::function<FunctionBuilderPtr(const Context &)>>
{
public:
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template <typename Function>
void registerFunction(CaseSensitiveness case_sensitiveness = CaseSensitive)
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{
registerFunction<Function>(Function::name, case_sensitiveness);
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}
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template <typename Function>
void registerFunction(const std::string & name, CaseSensitiveness case_sensitiveness = CaseSensitive)
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{
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if constexpr (std::is_base_of<IFunction, Function>::value)
registerFunction(name, &createDefaultFunction<Function>, case_sensitiveness);
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else
registerFunction(name, &Function::create, case_sensitiveness);
}
/// Throws an exception if not found.
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FunctionBuilderPtr get(const std::string & name, const Context & context) const;
/// Returns nullptr if not found.
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FunctionBuilderPtr tryGet(const std::string & name, const Context & context) const;
private:
using Functions = std::unordered_map<std::string, Creator>;
Functions functions;
Functions case_insensitive_functions;
template <typename Function>
static FunctionBuilderPtr createDefaultFunction(const Context & context)
{
return std::make_shared<DefaultFunctionBuilder>(Function::create(context));
}
const Functions & getCreatorMap() const override { return functions; }
const Functions & getCaseInsensitiveCreatorMap() const override { return case_insensitive_functions; }
String getFactoryName() const override { return "FunctionFactory"; }
/// Register a function by its name.
/// No locking, you must register all functions before usage of get.
void registerFunction(
const std::string & name,
Creator creator,
CaseSensitiveness case_sensitiveness = CaseSensitive);
};
}